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R&D Publications
Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2® and progestrone / Xu, Z.Z.; Burton, L.J.; MacMillan, K.L. 1997.
Theriogenology v.47 p.687-701
The objective of this study was to evaluate the reproductive performance of lactating cows in seasonal dairy herds after estrus synchronization with PGF2«alpha» (PG) with or without supplementation with progesterone (P4). In Trial 1, synchronized cows (S1; n = 521) were compared with untreated control cows (C; n = 518) in 5 herds. Estrus of cows in the S1 group was synchronized with 2 treatments of PG (Lutalyse) 13 d apart. The breeding season started 2 d after the second PG. Cows were first bred by AI for 7 wk and then herd sires were used. Compared with C cows, estrus synchronization in the treated cows reduced the conception rate to first AI (61.1 vs 70.5%; P < 0.01) and the intervals from start of the breeding season to conception for cows conceiving to AI (11.0 vs 14.6 d; P < 0.05) or to both AI and natural mating (16.5 vs 18.4 d; P < 0.05). There was no effect on conception rate to second AI (68.8%), on pregnancy rate by Day 24 (72.3%) or Day 49 (86.3%) of the breeding season, or on the percentage of cows not pregnant at end of the breeding season (5.0%). In Trial 2, effects of P4 supplementation before the second PG on reproductive performance were evaluated in 4 herds. Estrus of each cyclic cow was synchronized with PG as in Trial 1. Half of the cows in each herd were treated with an intravaginal P4 device (CIDR) for 5 d before the second PG (S2+P4, n = 608), whereas the remaining half received no CIDR treatment (S2, n = 593). Compared with S2 cows, P4 treatment increased the estrous response rate to the second PG (89.6 vs 82.9%; P < 0.01), the conception rate to first AI (65.1 vs 59.7%; P = 0.07), the pregnancy rate by Day 6 of the breeding season (59.3 vs 49.0%; P < 0.001), and reduced the intervals from start of the breeding season to conception for cows conceiving to AI (8.6 vs 10.4 d; P < 0.10) or to both AI and natural mating (12.7 vs 16.4 d; P < 0.01). Treatment with a used CIDR from Days 16 to 21 after start of breeding to resynchronize returns to service had no effect on conception rate to first or second AI but may decrease the conception rate to second AI in cows previously treated with CIDR. In conclusion, estrus synchronization with the double PG system can reduce fertility, while P4 supplementation for 5 d before the second PG can improve estrous response and overall reproductive performance. Stage of the estrous cycle at the time of the second PG can affect fertility following synchronization.
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Reproductive performance of lactating dairy cows following oestrus synchronisation with progesterone, oestradiol and prostaglandin / Xu, Z.Z.; Burton, L.J.; MacMillan, K.L. 1996.
New Zealand veterinary journal v.44 p.99-104
The ability to synchronise onset of oestrus, and hence the time of breeding and calving, offers potential economic and management benefits to dairy farmers, especially in herds with seasonally concentrated calving patterns. A trial involving 2681 cows in 11 seasonal herds was conducted to evaluate the reproductive performance of lactating dairy cows following oestrus synchronisation with a combination of progesterone, oestradiol and prostaglandin. Cows were randomly assigned within herds to synchronised and control groups, balanced for age, date of calving, body condition and breed. Cows in the synchronised group were treated with an intravaginal progesterone-releasing device containing 1.9 g of progesterone and a gelatin capsule containing 10 mg of oestradiol benzate 10 days prior to the planned start of the breeding season (day 0). The device was removed 8 days later on Day-2 and a luteolytic dose of prostaglandin F2a was adminstered 2 days prior to removal of the progesterone-releasing device. Returns to service for cows in the synchronised group were synchronised by inserting a previously used intravaginal device during Days 16-21 after the start of the breeding season. Cows in the control group were left untreated. The percentage of cows being inseminated during the first 5 days was 89.0% for the synchronised group compared to 29.7% for the control group. Compared to cows in the control group, those in the synchronised group had a lower conception rate to the first insemination (52.9% v. 64.3%, p<0.001), a lower conception rate to the second insemination (51.8% v. 62.5%, p<0.001), a higher percentage of empty cows at the end of the breeding season (7.3% v. 5.1%, p<0.05), and more insemination services per pregnancy to artificial insemination (2.0 v. 1.6, p<0.001). There was no difference between the synchronised and control groups in the percentage of cows pregnant to artificial insemination (8.18% v. 85.5%, p>0.10). The mean day of conception from the start of the breeding season was advanced (p<0.01) by 1.3 days in synchronised cows (19.9±0.7 days; mean±SEM) compared to control cows (21.2±0.5 days). It is concluded that the oestrus synchronisation regime used in the present study caused a reduction in fertility, which reduced the potential gains from using such a programme to increase reproductive efficiency in dairy cows.
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Reproductive performance of post-partum anoestrous dairy cows treated with with progesterone and oestradiol benzoate: correspondence / Xu, Z.Z.; Burton, L.J. 1997.
New Zealand veterinary journal v.45 p.213-214
During spring 1994-95 and 1995-96, in New Zealand, 15 anoestrous cows were fitted with a controlled internal drug-releasing (CIDR) device with a 10 mg oestradiol benzoate capsule for 5 days. 48 h after device removal (day 0) cows not in oestrus were given an injection of 1 mg oestradiol benzoate. Cows in oestrus were inseminated with frozen-thawed semen. On day 11, anoestrous cows were examined for the presence of a corpus luteum. Cows with a corpus luteum were injected with PGF |
Reproductive performance of synchronised lactating dairy cows / Xu, Z.Z.; Burton, J.R.; Burton, L.J.; MacMillan, K.L. 1995.
Proceedings of the New Zealand Society of Animal Production v.55 p.245-247
The objective of this trial was to evaluate the reproductive performance of lactating dairy cows following oestrous synchronisation with a combination of progesterone, oestradiol and prostaglandin. Cycling cows in 11 herds were randomly divided, with restriction to age, calving date, condition score and breed, into synchronised (n=1332) groups. Those in the synchronised group were each treated with an EAZI-BREEDŒ CIDR’ capsule for 8 days, with an injection of an analogue of prostaglandin F2alpha, 2 days prior to CIDR removal. Control cows were left untreated. Compared to the control cows, those in the synchronised group had a lower conception rate to the first round of AB (52.9% vs. 64.3%), a lower conception rate to all AB matings (53.2% vs. 63.9%), an increased number of AB services per pregnancy to AB (2.0 vs. 1.6), and an increased percentage of empty cows (7.3% vs. 5.1%). There was no difference between synchronised and control groups in the percentage of cows pregnant to AB (81.8% vs. 85.5%) or in the mean day of conception (20 vs. 21 days). The oestrous synchronisation regime tested in this study caused a reduction in fertility. This negated some of the potential gains from using such a treatment programme.
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Restricted maximum likelihood estimation of variance components for univariate animal models using sparse matrix techniques and average information / Johnson, D. L.; Thompson, R. 1995.
Journal of Dairy Science v.78 no.2 p.449-456
An algorithm is described to estimate variance components for a univariate animal model using REML. Sparse matrix techniques are employed to calculate those elements of the inverse of the coefficient matrix required for the first derivatives of the likelihood. Residuals and fitted values for random effects can be used to derive additional right-hand sides for which the mixed model equations can be repeatedly solved in turn to yield an average of the observed and expected second derivatives of the likeli- hood function. This Newton method, using average information, generally converges in 4 0 iterations. Although the time required per iteration is two to three times greater than that required per likelihood evaluation for derivative-free methods, the total time to convergence is generally much less. An example of a complex model, involving correlated direct and maternal genetic effects, and an additional uncorrelated random effect, indicates that REML, using average information, is about five times faster than a derivative-free algorithm, using the simplex method, which is about three times faster than an expectation-maximization al-gorithm.
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Review of QTL mapping in the New Zealand and Dutch dairy cattle populations / Spelman, R.J.; Coppieters, W.; Grisart, B.; Blott, S.; Georges, M. 2001.
Proceedings of the 14th AAABG conference p.11-16
A joint venture between Livestock Improvement and Holland Genetics where monetary, biological and data resources were pooled, has proven successful in identifying QTL through work undertaken at the University of Liege. The majority of the work has been undertaken with a granddaughter design where 31 families have been genotyped with over 300 microsatellites and single nucleotide polymorphisms. Four QTL for milk production are reported in this paper; on chromosomes 6, 14, 16 and 20. Fine mapping has been undertaken for these QTL, with the QTL identified on chromosome 14 being fine mapped to a very defined region. QTL for non-production traits have been identified but differ between the New Zealand and Dutch dairy populations. The milk production QTL have been utilised in both of the companies breeding schemes via marker assisted selection.
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Risk factors associated with the incidence of ketosis in dairy cows / Rasmussen, L.K.; Nielsen, B.L.; Pryce, J.E.; Mottram, T.T.; Veerkamp, R. F. 1999.
Animal science v.68 p.379-386
Data collected at the Langhill Dairy Cattle Research Centre, UK, from January 1980 to December 1996 were analysed to identify ketosis risk factors. The data covered 3586 lactations and included 175 incidents of ketosis. Two approaches were used to assess the relative risk to cows of contracting ketosis, one using information known at the beginning of lactation and the other using information collected as the lactation progressed. In both approaches analyses were carried out using different amounts of the available information to simulate differences between recording systems. In the first approach the following were found to relate significantly to the level of recorded ketotic incidents: parity, ketosis in the previous lactation, calving condition score, 305-day milk yield in the previous lactation and the average milk protein percentage in the previous lactation. The effects of these were quantified. In the second approach, where the change in ketosis incidence rate over the weeks of lactation was investigated, the average dry-matter intake in the previous week and changes in liveweight and body condition score over the previous week were found to have a significant effect on the probability of getting ketosis in the coming week. The risk assessments varied depending on the information used and a flexible approach is recommended if potential risk factors are to be successfully incorporated into decision support systems.
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Rotation crosses and inter se matings with angus and hereford cattle for five generations / Morris, C.A.; Baker, R.L.; Cullen, N.G.; Johnson, D.L. 1994.
Livestock Production Science v.39 p.157-172
A total of 3768 calves and 4950 cow mating-years were involved in a study of heterosis retention. Crosses included first and subsequent inter-crosses between Angus and Hereford breeds as far as the fifth calf generation (F1, F2,...F5), back crosses (B1) using both F1 sires and F1 dams, and rotation crosses as far as the fifth calf generation (R2, R3, R4 and R5). Records collected were calf traits to the yearling stage, cow reproduction and maternal traits, and steer carcass data. Effects were estimated for 27 breed types for calves and 23 for cows. Breed type effects were then replaced by multiple regression coefficients for genetic effects including: an average individual (Angus) breed effect (gI), average maternal (gM) and average grandmaternal (gMG) breed effects, individual (dI), maternal (dM) and paternal (dP) dominance effects, and epistatic effects. From these, individual (hI) and maternal (hM) heterosis and other parameters were derived. For the Angus breed, gI was generally negative and gM positive for direct calf weights and cow weight; gI was positive for calf weaning weight (WW) as a maternal trait. The Angus breed was superior to the Hereford for net reproduction, productivity (weight of calf weaned per cow mated) and an efficiency ratio (productivity/average cow weight). Relative to the average of the purebreds, the superiorities of F1, F3 to F5, and R4 animals were respectively 2.1, 3.2 and 5.0% for birth weight, 6.5, 3.7 and 7.9% for yearling weight, 6.7, -2.2 and 3.4% for cow weight, 10.3, 0.7 and 11.7% for calf WW as a maternal trait, 7.4, -1.3 and 5.7% for number of calves weaned per cow mated, 19.4, 1.0 and 18.4% for productivity, and 11.2, 2.1 and 14.0% for the efficiency ratio. For calf traits and cow weight, dM and hI were generally significant and positive (except negative for calving date), whilst only hI was generally significant for calf weights as maternal traits. For the reproductive traits, the trends were for hI to be positive, but standard errors were large. For carcass traits, the interbreds and rotation crosses were generally like the heavier, fatter (i.e. Hereford) purebred. Overall, for productivity and the efficiency ratio, the rotation crosses (especially R4) were superior to the purebreds but generally not to the F1s, whilst the interbreds were similar to the purebred average.
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Seasonal variation in testis size, gonadotrophin secretion & pituitary responsiveness to gnrh in rams of two breeds differing in. / Xu, Z.Z.; McDonald, M.F.; McCutcheon, S.N.; Blair, H.T. 1991.
Animal reproduction science v.26 p.281-292
Six Romney and 6 Poll Dorset rams, aged 2 yr, were studied from Sep. 1988 to Mar. 1989. During this period, testes diameter and body weight were measured at 2- to 3-wk intervals. In Sep., Nov., Dec., Feb. and Mar., the animals were bled intensively for plasma LH and FSH assay, and after GnRH treatment for plasma FSH assay. Testes diameter showed a seasonal trend, being higher during the breeding season than at other times. Poll Dorsets showed less seasonal variation in testes diameter than Romneys. Breed significantly affected testes diameter in all seasons, being higher in Poll Dorsets than in Romneys. In the Poll Dorsets, testes diameter increased earlier in the breeding season than in the Romneys. During all sampling months, Romney rams had higher plasma LH levels and plasma LH pulse frequencies than Poll Dorset rams. Sampling month and breed x sampling month interaction significantly affected LH pulse frequency. Plasma FSH level was significantly affected by sampling month, the increase in plasma FSH level occurring earlier in the breeding season in Poll Dorsets than in Romneys. Sampling month, but not breed or breed x sampling month interaction, significantly affected GnRH-stimulated total LH level and peak LH level
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Selection for reduced gestation length in New Zealand dairy cattle / Winkelman, A.M.; Spelman, R.J. 2001.
Proceedings of the 14th AAABG conference p.63-66
Detection of loci that affect quantitative traits (QTL) such as milk production has been undertaken with daughter and grand-daughter designs in the N.Z. dairy industry. This paper outlines and discusses relative statistical powers and costs of these and other experimental designs. The grand-daughter design involves genotyping a grandsire and his progeny tested sons whereas the daughter design comprises a sire and his daughters genotyped for molecular markers spaced across the genome.Significant differences in mean estimated breeding value between the two progeny groups that inherited alternate sire alleles at a marker locus indicate the presence of a linked QTL. The grand-daughter design has 3-4 times more power per genotype than the daughter design due to greater accuracy in evaluation of progeny tested bulls than lactating cows. To increase the power per genotype in the daughter design, only daughters at the extremes (high and low) of the trait distribution are selected and individually genotyped (selective genotyping). An extension is DNA pooling where DNA from daughters at each extreme of the distribution is pooled. The frequency of the two sire alleles for each genetic marker are measured and when significantly different than the expected 0.5 in one of the pools a linked QTL is identified. QTL effects can be estimated by relating the difference in allele frequencies with the difference in trait value between the two pools. With large half-sib families selective DNA pooling has power to identify a large proportion of the QTL contributing to the genetic variance with relatively low genotyping requirements. A sire family of 100,000 with the top and bottom 1% of progeny pooled has the same power as approximately 12,000 progeny being individually genotyped with less than 1% genotyping effort. Crossbreeding in the New Zealand dairy industry opens up the opportunity to identify QTL alleles that contribute to the genetic differences between the two breeds. Identification of breed specific QTL alleles can be achieved with power of 90% with some 800-1300 progeny from matings of F1 Holstein-Friesian x Jersey bulls to F1 cows.
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Selection to increase the b-lactoglobulin B variant in New Zealand dairy cattle / Harris, B.L. 1997.
FIL/IDF Milk Protein Polymorphims Conference: Christchurch p.467-473 The economic returns from milk products depend on the quantity and the processing characteristics of the milk. Milk containing different genetic variants of ß-lactoglobulin are known to influence milk powder and cheese manufacturing properties. The milk from BB ß-lactoglobulin genotypes provides increased cheese yield and improved efficiency of manufacture for milk powders from less fouling and changes to the viscosity. There have been three genetic variants found for ß-lactoglobulin in the New Zealand dairy cattle population. A, B and C. The C variant is only in Jersey cattle at a low frequency, less than 8%. The A variant has a frequency of 30% and 28% in the Jersey and Holstein-Friesian populations, the B variant has a frequency of 62% and 72%, respectively. To increase the freqency of the B variant in the national population the national selection programme should look at the consequences of including ß-lactoglobulin genetic variant in the selection criteria. This would allow simultaneous genetic improvements in milk quantity and quality. The current national selection criteria include milk volume, milkfat and milk protein yields, liveweight and survival. Allowing selection for ß-lactoglobulin would reduce the selection intensity placed on the traits currently in the selection objective and hence, lower the economic response from these traits. The economic response from selection for ß-lactoglobulin would need to offset the loss in the economic response from the current traits and cover the costs of implementation in the national breeding scheme to be economically viable.
The breeding objectives model used to determine economic weights for quantitative traits was extended to incorporate qualitative traits allowing the incorporation of ß-lactoglobulin genotype in the national selection index. Methods and the resulting economic weights are discussed.
A stochastic breeding scheme model was used to determine the response to selection over 20 years in the current traits and the change in gene frequency of the ß-lactoglobulin genetic variants from four selection policies:
(1) No selection for ß-lactoglobulin genotype.
(2) Preselection of BB ß-lactoglobulin genotypes in three reproductive pathways: cows to breed bulls, bull to breed bulls, and bulls to breed cows.
(3) Preselection of BB and AB ß-lactoglobulin genotypes in three reproductive pathways” cows to breed bulls, bull to breed bulls and bulls to breed cows.
(4) Index selection including ß-lactoglobulin.
Results from the breeding scheme model are presented.
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Selective genotyping to detect Quantitative Trait Loci for multiple traits in outbred populations / Bovenhuis, H.; Spelman, R. 2000.
Proceedings: 6th World Congress on Genetics Applied to Livestock Production v.26 p.241-244 Selective genotyping i.e, the genotyping of individuals that are extreme for a quantitative trait, has been undertaken in many studies but has usually been limited to one trait of interest. This paper outlines the implications of selective genotyping for traits that are correlated to the trait that selective genotyping was undertaken. Formulas are presented that enable unbiased estimation of QTL effects for the selectively genotyped and correlated traits. Further, power calculations for the selectively genotyped trait and correlated traits are demonstrated with an example.
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Selective genotyping to detect Quantitative Trait Loci for multiple traits in outbred populations / Bovenhuis, H.; Spelman, R. 2000.
Journal of dairy science v.83 p.173-180
Selective genotyping (i.e., genotyping of individuals that are extreme for a quantitative trait) has been undertaken in many studies but has usually been limited to one trait of interest. This paper outlines the implications of selective genotyping when applied to a daughter design. Formulas are presented that enable unbiased estimation of QTL effects for the selectively genotyped and correlated traits. Formulas were verified using simulation. Further, formulas are presented to enable power calculations to be undertaken for the selectively genotyped trait and correlated traits. These algorithms are demonstrated with a numerical example.
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A semen allocation system for Livestock Improvement: a case study in goal programming / Irwin, S.C.; Scott, J.L.; Jackson, R.G. 1996.
Computers and electronics in agriculture v.16 p.87-101
A goal programming model was developed to support an AI programme with semen from proven bulls. The programme rosters bulls for semen collection to meet the given demand. The 1st objective of the rostering is to maximize dairy farm income through maximizing genetic progress in the New Zealand national herd. Once this maximum has been fixed, the 2nd-ranked objective of maintaining the financial viability of the Livestock Improvement Corporation is maximized. A goal programming model was used to assign semen to technologies (fresh or frozen semen), across specified periods, in order to meet demand and maximize the objective functions. The results showed that the number of bulls from which semen is collected can be reduced. For Holstein sires in 1991, the model predicted improvement of discounted cash flows to farmers by 5.8% relative to current practice
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Sperm numbers, semen age and fertility in fresh and frozen bovine semen / Vishwanath, R.; Pitt, C.J.; Shannon, P. 1996.
Proceedings of the New Zealand Society of Animal Production v.56 p.31-34
The consequence of a seasonal mating pattern is that a significant amount of semen from the top sires is required during this intensive mating period to satisfy the demand. To utilise semen from these top sires efficiently, liquid semen technology has been extensively used in New Zealand. This paper describes the essential physiological differences between liquid and frozen semen and their relative advantages and disadvantages. Alternative technologies such as freezing semen in bulk and later rediluted for use as liquid semen can be used to overcome the constraints of an intensive mating season.
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Storage of bovine semen in liquid and frozen state / Vishwanath, R.; Shannon, P. 2000.
Animal reproduction science v.62 p.23-53
This review describes the historical and current methods used for storage of bovine semen. The essential physiological differences between liquid and frozen semen, their relative advantages and disadvantages are addressed, and the current state of technology, the procedures used, their merits and future possibilities are also discussed.
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Synchronization of estrus with PGF2a administered 18 days after a progesterone treatment in lactating dairy cows / Xu, Z.Z.; Burton, L.J. 1998.
Theriogenology v.50 p.905-915
In a previous study we showed that estrus synchronization with 2 treatments of PGF2«alpha» 13 d apart reduced conception rate at the synchronized estrus and that this reduction occurred mainly in cows in the early luteal phase at the second PGF2«alpha» treatment. The objective of the present study was to determine the efficacy of a synchronization regimen in which PGF2«alpha» was administered during the mid- to late-luteal phase to cows that had previously been synchronized with progesterone. Spring-calving cows from 6 dairy herds were used in this study. On Day -32 (Day 1 = the start of the breeding season), cows that had calved 2 or more weeks ago were randomly assigned to a synchronization (S, n = 732) or control (C, n = 731) group. Cows in Group S were treated with an intravaginal progesterone device (CIDR) for 12 d from Day -32 to Day -20, while those in Group C were left untreated. Similar percentages of cows in Group S (80.6%) and C (82.9%) had cycled by Day -7. The CIDR treatment synchronized the onset of estrus, resulting in 92.9% of cows in estrus being detected within 7 d after CIDR removal. Cows in Group S that had cycled by Day -7 were treated with PGF2«alpha» (25 mg, im, Lutalyse) on Day -2. Cows in both groups that were anestrous on Day -7 were treated with a combination of progesterone and estradiol benzoate (EB) to induce estrus and ovulation (CIDR and a 10 mg EB capsule on Day -7, CIDR removal on Day -2, and injection of 1 mg EB 48 h after CIDR removal). The PGF2«alpha» treatment synchronized the onset of estrus in 87.5% of the cows. Group S and C cows had similar conception rates to first (61.0 vs 58.3%) and second (58.4 vs 60.9%) AI; similar pregnancy rates over the AI period (82.8 vs 79.2%) and over the whole breeding season (91.9 vs 90.6%); and required a similar number of services per pregnancy to AI (1.7 vs 1.8). The interval from the start of the breeding season to conception for cows conceiving to AI or to combined AI and natural mating was shorter (P < 0.001) by 5.7 and 6.2 d, respectively, for the Group S cows. It is concluded that the treatment regimen tested in the present study achieved satisfactory estrus synchronization, had no detrimental effect on fertility at the synchronized estrus, and shortened the interval from start of the breeding season to conception.
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Testis size and endocrine parameters in rams as predictors of aseasonality in their daughters / Xu, Z.Z.; McDonald, M.F.; McCutcheon, S.N.; Blair, H.T. 1992.
Proceedings of the New Zealand Society of Animal Production v.52 p.195-198
A progeny test involving Romney (n=5) and Poll Dorset (n+5) rams mated to Romney ewes was conducted to examine the relationship between testis size and endocrine parameters, measured during the transitional period from the non-breeding to the breeding season, in rams, and reproductive performance of their daughters in the first and second breeding seasons. More of the Poll Dorset cross hoggets reached puberty during the first breeding season (80 v. 60%; P<0.01) associated with earlier onset (13 v. 22 May; P<0.10) at younger ages (264 v. 276 days; P<0.10) and more oestrous cycles (2.7 v. 2.0; P<0.05) than for Romney hoggets. The date of onset of the second breeding season was influenced by breed (P<0.001) and sire within breed (P<0.05). These differences between Romney and Poll Dorset cross animals in reproductive performance were associated with differences between their sires in the pattern of seasonal variation in testis size and plasma gonadotrophin concentrations. However, within-breed correlations between testicular and endocrine parameters in the sires and date of onset of the breeding season in the offspring were low. It is concluded that, while some of the testis and endocrine parameters could potentially be used as selection criteria for date of onset of the breeding season in ewes, further studies are needed before these parameters can be incorporated into selection programmes
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Testis size, gonadotrophin secretion and pituitary responsiveness to GnRH in Romney rams during the transition from the non-breeding to the breeding season / Xu, Z.Z.; McDonald, M.F.; McCutcheon, S.N.; Blair, H.T. 1993.
Animal Reproduction Science v.31 p.99-111
Romney rams, which had an early (n =7) or a late (n =5) increase in testis size prior to the onset of the breeding season, were selected from a larger population (n =60). In the following year, 2 groups were compared for the pattern of seasonal variation in testis size, plasma gonadotropin concentration and pituitary responsiveness to a GnRH challenge during the transitional period from the non-breeding to the breeding season. Rams in the early-increase group had an earlier and greater increase in testis size than rams in the late-increase group; this pattern was largely repeatable between years. Differences between groups in the pattern of seasonal variation in testis size were associated with group differences in endocrine function. Thus, rams in the early-increase group had higher (P <0.01) LH pulse frequency in Mar. than those in the late-increase group (4.4 plus or minus 0.4 vs. 1.7 plus or minus 0.3 pulses per 8 h) and the seasonal increase in plasma FSH concentration occurred earlier (P <0.10) in the early group than in the late group. There were also group differences in the pattern of seasonal variation in total LH response to the GnRH challenge. The results showed that there are differences among rams within breed, in the pattern of seasonal variation in testis size and gonadotropin secretion.
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Treatment of noncyclic lactating dairy cows with progesterone and Estradiol or with progesterone, GnRH, prostaglandin F2a and Estradiol / Xu, Z.Z.; Burton, L.J.; McDougal, S.; Jolly, P.D. 2000.
Journal of dairy science v.83 no.3 p.464-470
The efficacy of two programs for treating noncyclic cows was compared. In trial 1, 478 cows in five herds were randomly divided into two groups. Cows in one group (C group) were treated with an intravaginal progesterone device for 8 d followed in 48 h by 1 mg of estradiol benzoate to cows that had not been detected in estrus since device removal. Those in the other group (CGP group) were treated with progesterone and estradiol as for the C group plus 10 µg of a GnRH agonist (buserelin) at device insertion and 25 mg of PGF2a 7 d after device insertion. In trial 2 with 729 cows in nine herds, the treatments were similar to those in trial 1 except that the duration of progesterone treatment was 7 d. No significant difference was found between trials and results from both trials were combined. Compared with C group cows, CGP group cows had a greater estrous response rate (93.2 vs. 89.1%), a greater conception rate to first artificial insemination (AI, 47.1 vs. 29.4%), marginally lower conception rate to second AI (52.9 vs. 59.7%), lower nonpregnancy rate (8.3 vs. 11.1%), and shorter intervals from the start of breeding to conception by AI (9.8 vs. 15.3 d) or by AI or natural mating (21.6 vs. 26.3 d). The treatment protocol used for the CGP group achieved better reproductive performance than that used for the C group.
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Treatment of noncycling cows. / Rhodes, F.M.; McDougal, S.; Verkerk, G.A.; Xu, Z.Z.; Cullum, A. 2000.
Proceedings of a Seminar of the Society of Dairy Cattle Veterinarians of the New Zealand Veterinary Association v.17 p.125-134
A series of field trials have been conducted to evaluate a variety of treatment protocols for dairy cows which have not been seen in oestrus (NDO) by the start of mating. Results of these trials are presented in this paper.
Treating NDO cows which had a detectable corpus luteum (CL + ve) with a combination of oestradiol benzoate (ODB), progestrerone (P4) and prostaglandin F2a (PGF) did not improve conception or pregnancy rates, compared with leaving them untreated.
The effectiveness of using GnRH in combination with P4, PGF and ODB for the treatment of anovulatory anoestrous (AA) cows was compared with the standard P4 and ODB protocol. In addition, the effectiveness of the GnRH programme in NDO CL + ve cows was compared with no treatment. In AA cows, there was no difference in reproductive performance following the GnRH programme compared with the standard protocol. In contrast, treatment of NDO CL + ve cows with the GnRH programme significantly improved submission and pregnancy rates compared with no hormonal treatment.
Treatment of AA cows with GnRH, PGF and GnRH (‘Ov-synch’ protocol) resulted in similar submission rates and pregnancy rates compared with using P4 and ODB.
The effect of grazing NDO cows separately from the main herd from 7 days before, to 21 days after the planned start of mating, was examined in combination with hormonal treatment. Separate grazing did not improve submission rates or conception rates of AA cows compared with grazing in the main herd, however, pregnancy rates after 21 days of mating were significantly reduced. The reproductive performance of NDO CL + ve cows did not differ when grazed separately when compared with grazing in the main herd.
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Treatment of post-partum anoestrous dairy cows with progesterone,oestradiol and equine chorionic gonadotrophin / Xu, Z.Z.; Burton, L.J.; MacMillan, K.L. 1997.
New Zealand veterinary journal v.45 p.205-207
Anoestrus in lactating dairy cows at the start of the breeding season is a major form of reproductive wastage for seasonal dairy production based on pasture. The objective of this study was to compare the reproductive performance of anoestrous cows that were treated with a combination of progesterone, oestradiol and equine chorionic gonadotrophin either 10 days before (T – 10, n = 219) or 16 days after (T+16, n = 229) the start of the breeding season. A higher percentage of cows in the T–10 group were detected in oestrus and inseminated during the first 6 days of breeding than those in the T+16 group (69.4% v. 26.2%, p<0.001). However, the percentage of cows detected in oestrus by Day 16 was similar between the two treatment groups (T-10 v. T+16; 77.7% v. 76.7%). There was no difference between treatment groups in conception rate to the first (51.2% v. 59.0%) or the second insemination (50.8% v. 57.6%), in pregnancy rate over the first 49 days (74.0% v. 75.1%), in empty rate (10.0% v. 10.5%) or in the mean day of conception from the start of the breeding season (24.0 v. 25.7 days). These results suggest that, under favourable environmental conditions, treatment of anoestrous cows with the programme used in this trial can be performed 16 days after the start of the breeding season with similar results to that performed 10 days before the start of the breeding season. Further studies are needed to determine if this is the case under different environmental conditions of for other treatment programmes.
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Utilisation of genetic variation by marker assisted selection in commercial dairy cow populations / Spelman, R.J.; Garrick, D.; Van Arendonk, J.A.M. 1999.
Livestock Production Science v.59 no.1 p.51-60
Potential genetic benefits of marker assisted selection (MAS) were evaluated by calculating selection response resulting from four pathways of selection. Genetic variation was partitioned into polygenic and loci that were in linkage disequilibrium with marker loci or haplotypes. The percentage of genetic variation that was marked was varied from 0 to 100%. These assumptions describe the degree of genetic knowledge that may be available in 10 years. Three breeding strategies with markers were evaluated: progeny test scheme (BMARK); progeny test scheme but unproven bulls allowed on the bull to bull selection path (YBULL); and a breeding programme where cows without lactation information and bulls without progeny information were eligible for selection (OPEN). Rates of genetic gain (per year) with no marked genetic variance were 0.26 G for the BMARK and YBULL schemes and 0.28 G for the OPEN scheme. On average, an increase of 1% marked genetic variance resulted in an increase in genetic gain of ~0.25% for the BMARK scheme, 0.5% for the YBULL scheme and 1% for the OPEN scheme. Maximum genetic response (100% marked genetic variance) for the BMARK scheme was 1.24 times that achieved with no marked genetic variance, 1.52 times for the YBULL scheme, and 2.05 times for the OPEN scheme. Changes in the structure of the breeding scheme are needed to fully gain the benefits of identified loci especially for medium to large proportions of marked genetic variance.
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Utilisation of marker assisted selection in a commercial dairy cow population / Spelman, R.; Garrick, D. 1997.
Livestock Production Science v.47 no.2 p.139-147
Genetic and economic benefits of marker assisted selection (MAS) to a commercial dairy cow population were evaluated by calculating selection advance resulting from four pathways of selection. In addition to background polygenic effects, a single additive quantitative trait loci (QTL) was segregating. Three sizes of QTL were assessed; 0.5, 1.0 and 2.0 genetic standard deviations (G) (difference between homozygotes), at each of four starting QTL frequencies; 0.01, 0.10, 0.35 and 0.75 over a thirty year time horizon. No recombination existed between QTL and a marker. Two MAS strategies were evaluated by comparison to a breeding scheme that had no genotypic knowledge of the QTL, over a thirty year time horizon. Economic benefits were calculated from the returns of extra milk produced (accounting for increased feed costs) less identification costs of the QTL and subsequent genotyping costs. In both strategies increase in QTL frequency was not immediate and thus returns were received in the later years of the analysis. The MAS strategy that utilised knowledge of QTL genotype for bull dams and bull sires had superior genetic gain at all QTL sizes and frequencies. However, it was only profitable for a 1.0 G QTL at 0.1 and 0.35 frequencies, and a 2.0 G QTL at all except the highest frequency (0.75). Long-term genetic loss was observed. The second MAS strategy of progeny testing only homozygous and heterozygous QTL bulls required a QTL of size 1.0 G at frequencies of 0.1 or 0.35 or a 2.0 G QTL at frequencies of 0.01, 0.1 and 0.35 to be more profitable than the current breeding scheme. The choice of MAS strategy should depend on QTL size and frequency.
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