Factors affecting commercial application of embryo technologies in New Zealand: a modelling approach

New reproductive technologies include sexed sperm and embryo-based technologies. The technology of sperm sexing, for various reasons, is not available in New Zealand and its use has not been modelled. Embryo technologies are however already in use on a limited scale and various scenarios for their use in both the dairy and beef industries in New Zealand have been modelled. This review briefly discusses the various technologies available and some of their potential strengths and weaknesses. In the dairy industry, modelling has been used to simulate the production of breeding bulls for large breeding companies and the production of replacement heifers in dairy herds. For the beef industry, similar modelling has been carried out to determine the opportunities for more efficient beef production.All the models confirmed that at current levels of performance, embryo-based reproductive technologies are usually not profitable in New Zealand except in niche market situations where the returns from the resulting offspring are significantly greater than can be obtained from natural mating or artificial insemination (AI) reproduction systems. This is confirmed by the low uptake of these technologies in this country to date. Even if performance lifts to levels similar to AI, profitability is likely to occur only if the costs of pregnancies to embryo-based reproductive technologies can occur at prices less than two to four times greater than AI or natural mating. This break-even requirement depends on the returns that can be achieved and the advantages that can be captured by the technology over and above those available from AI or natural mating. Two new uses for reproductive technologies in dairy cattle could be the proliferation of novel or rare genotypes from gene discovery programs and improving the female reproductive rate for optimal marker assisted selection. In both these uses the technology is not at present competing with AI or natural mating. The challenge exists therefore for the biological scientists to satisfy these requirements, coupled with the ethical and human factors involved in the introduction of any new technology.Potential end users of the technologies have been surveyed. They are quite positive about the technologies provided they can use them profitably and are keen to obtain more information about them.     

Economics of selecting for sex: the most important genetic trait

Over 20,000 calves have resulted from artificial insemination (AI) of cattle with sexed, frozen/thawed sperm in the course of experimentation in several countries, and from commercial sales in the United Kingdom. This technology likely will become commercially available in many countries within a few years. Accuracy of the process is about 90% for either sex, and resulting calves appear to be no different from non-sexed controls in birthweight, mortality, rate of gain, and incidence of abnormalities. The main determinants of the extent of use of sexed sperm will be pregnancy rate and cost. Fertility of low doses (1.5 x 10(6)-2 x 10(6)) of sexed, frozen sperm for AI of heifers usually has been in the range of 70-80% of unsexed sperm at normal doses (10 x 10(6)-20 x 10(6) sperm) in well managed herds; it has been lower in poorly managed herds, and likely will be lower with lactating dairy cows. It is expected that fertility of sexed sperm will increase significantly due to very recent improvements in the hydrodynamics of the sexing process and potential improvements in cryopreservation procedures. It is unclear how sexed sperm will be priced; the cost of sexed sperm for cattle will likely be more than double the cost of unsexed sperm in most markets. The economic benefit of using sexed sperm also will depend on the baseline fertility of the herd since at lower fertility, it takes more doses of semen per calf produced. It is noted that for a small percentage of elite cattle, the economics of using sexed sperm do not depend primarily on increased production or efficiency of producing meat or milk, but rather on factors such as scarcity, tradition, cattle show winnings, and biosecurity during herd expansion. Until sorting efficiencies improve and costs decline, sales likely will be limited primarily to these niche markets. With near normal fertility and a premium for sexing in the range of US$ 10 per insemination dose, sexed sperm likely would become economically and environmentally beneficial for many, if not most populations of cattle being bred by AI.     

Questionnaire identifying management practices surrounding calving on spring-calving dairy farms and their associations with herd size and herd expansion

Healthy calves are fundamental to any profitable dairy enterprise. Research to-date, has focused on year-round calving systems which experience many different challenges compared to spring-calving systems. The objective of the present study was to determine the on-farm dry cow, calving, and colostrum management practices of spring-calving dairy production systems, and quantify their associations with herd size and herd expansion status (i.e. expanding or not expanding). Information on these management practices was available from a survey of 262 Irish spring-calving dairy farmers, representative of the Irish national population. Herd expansion in the 2 years before, and the year that the survey was conducted was not associated with any of the management practices investigated. Fifty-three percent of respondents had an average calving season length of 10 to14 weeks with 35% of herds having a longer calving season. Previous research in cattle has documented that both colostrum source and feeding management are associated with the transmission of infectious disease from cow to calf. In the present study 60% of respondents fed calves colostrum from their own dam; however, 66% of those respondents allowed the calf to suckle the dam, 23% of survey respondents fed calves pooled colostrum. Larger herds were more likely (P<0.01) to use pooled colostrum supplies, while smaller herds were more likely (P<0.05) to allow the calf to suckle the dam. The majority (86%) of respondents had stored supplies of colostrum; average-sized herds had the greatest likelihood of storing colostrum (P<0.05), compared to other herd sizes; larger sized herds had a lesser likelihood (P<0.05) of storing colostrum in a freezer, compared to other herd sizes. Although freezing colostrum was the most common method used to store colostrum (54% of respondents), 17% of respondents stored colostrum at room temperature, 29% of which stored it at room temperature for greater than 4 days. The results from the present study indicate that a particular focus needs to be placed on calving and colostrum management because this study has highlighted a number of areas which are below international standards, and may have repercussions for calf health. Furthermore, management practices on larger farms could be improved and, as these represent the future of dairy farming, a focus needs to be placed on them. Expanding herds are not a particular concern as herd expansion, independent of herd size, does not seem to be associated with calving and colostrum management practices on Irish spring-calving dairy herds.     

Relationship between dairy cow genetic merit and profit on commercial spring calving dairy farms

Because not all animal factors influencing profitability can be included in total merit breeding indices for profitability, the association between animal total merit index and true profitability, taking cognisance of all factors associated with costs and revenues, is generally not known. One method to estimate such associations is at the herd level, associating herd average genetic merit with herd profitability. The objective of this study was to primarily relate herd average genetic merit for a range of traits, including the Irish total merit index, with indicators of performance, including profitability, using correlation and multiple regression analyses. Physical, genetic and financial performance data from 1131 Irish seasonal calving pasture-based dairy farms were available following edits; data on some herds were available for more than 1 year of the 3-year study period (2007 to 2009). Herd average economic breeding index (EBI) was associated with reduced herd average phenotypic milk yield but with greater milk composition, resulting in higher milk prices. Moderate positive correlations (0.26 to 0.61) existed between genetic merit for an individual trait and average herd performance for that trait (e.g. genetic merit for milk yield and average per cow milk yield). Following adjustment for year, stocking rate, herd size and quantity of purchased feed in the multiple regression analysis, average herd EBI was positively and linearly associated with net margin per cow and per litre as well as gross revenue output per cow and per litre. The change in net margin per cow per unit change in the total merit index was €1.94 (s.e. = 0.42), which was not different from the expectation of €2. This study, based on a large data set of commercial herds with accurate information on profitability and genetic merit, confirms that, after accounting for confounding factors, the change in herd profitability per unit change in herd genetic merit for the total merit index is within expectations.     

Evaluating the success of sex-sorted semen in US dairy herds from on farm records

These data summarize on-farm records of dairy herds (n = 211) using sexed semen. Sexed semen was predominantly used at first and second service in virgin heifers, which is reflected in younger ages at AI and at calving. Conception rates at first service averaged 47% for Holstein heifers and 53% for Jersey heifers, which were ∼80% of that achieved with conventional semen. Analysis of inter-estrus intervals provides no evidence that cycle lengths are extended by use of sexed semen. Among singleton births, 89% were reported as female offspring and this rises to 90% for gestation lengths within a normal 265-295 d range. Age at calving appeared to interact with calf sex and semen type to influence the incidence of stillbirths. Semen type had no effect on the incidence of stillbirths among heifers delivering female calves. However, the incidence of stillbirths among heifers delivering male calves was greater for those conceived from sexed semen and was only partially explained by age at calving. Because the incidence of male calves from sexed semen is only 10%, the total incidence of stillbirths was not affected by semen type. In conclusion, failure to differentiate sexed from conventional semen in data recording and preferential bias in use of sexed semen in younger, more fertile females makes legitimate comparisons of sexed and conventional semen in the commercial setting difficult. When used in Holstein heifers, the average first service conception rate achieved with sex-sorted semen was 47%, which appeared to ∼80% of that achieved with conventional semen in the same herds. The percentage of female calves (89%) was consistent with expectations. After adjusting for age at calving, sexed semen had no affect on the total incidence of stillbirths, however the source for an apparent increased incidence of stillbirth among male calves born from X-sorted sperm populations requires further investigation.     

Associations between herd size, rate of expansion and production, breeding policy and reproduction in spring-calving dairy herds

Dairy herd size is expected to increase in many European countries, given the recent policy changes within the European Union. Managing more cows may have implications for herd performance in the post-quota era. The objective of this study was to characterise spring-calving herds according to size and rate of expansion, and to determine trends in breeding policy, reproduction and production performance, which will inform industry of the likely implications of herd expansion. Performance data from milk recording herds comprising 775,795 lactations from 2,555 herds for the years 2004 to 2008 inclusive were available from the Irish Cattle Breeding Federation. Herds were classified into Small (average of 37 cows), Medium (average of 54 cows) and Large (average of 87 cows) and separately into herds that were not expanding (Nil expansion), herds expanding on average by three cows per year (Slow expansion) and herds expanding on average by eight cows per year (Rapid expansion). There was no association between rate of expansion and 305-day fat and protein yield. However, 305-day milk yield decreased and milk protein and fat percentage increased with increasing rate of expansion. There were no associations between herd size and milk production except for protein and fat percentage, which increased with increasing herd size. Average parity number of the cows decreased as rate of expansion increased and tended to decrease as herd size increased. In rapidly expanding herds, cow numbers were increased by purchasing more cattle. The proportion of dairy sires relative to beef sires used in the breeding programme of expanding herds increased and there was more dairy crossbreeding, albeit at a low rate. Similarly, large herds were using more dairy sires and fewer beef sires. Expanding herds and large herds had superior reproductive performance relative to non-expanding and small herds. Animals in expanding herds calved for the first time at a younger age, had a shorter calving interval and were submitted for breeding by artificial insemination at a higher rate. The results give confidence to dairy producers likely to undergo significant expansion post-quota such that, despite managing more cows, production and reproductive performance need not decline. The management skills required to achieve these performance levels need investigation.     

Applications of sexed semen in cattle production

Sexed semen will contribute to increased profitability of dairy and beef cattle production in a variety of ways. It could be used to produce offspring of the desired sex from a particular mating to take advantage of differences in value of males and females for specific marketing purposes. Commercial dairy farmers, those who produce and market milk, could use sexed semen to produce replacement daughters from genetically superior cows and beef crossbred sons from the remainder of their cow population. To increase the rate of response to selection, seedstock dairy cattle breeders could produce bulls for progeny testing from a smaller number of elite dams by using sexed semen to ensure that all of them produced a son. Using sexed semen could then reduce the cost of progeny testing those bulls, because fewer matings would be necessary to produce any required number of daughters. Commercial beef cattle farmers, producing animals for eventual slaughter, could use sexed semen to capitalize on the higher value of male than female offspring for meat production. They could also use sexed semen to produce specialized, genetically superior replacement heifers from as small a proportion of the herd as possible. This would allow the remainder of the herd to produce male calves from bulls or breeds with superior genetic merit for growth, feed conversion efficiency, and carcass merit. Single-sex, bred-heifer systems, in which each female is sold for slaughter soon after weaning her replacement daughter, would be possible with the use of X-chromosome-sorted semen. Use of sexed semen would make terminal crossbreeding systems more efficient and sustainable in beef cattle. Fewer females would be required to produce specialized maternal crossbred daughters, and more could be devoted to producing highly efficient, terminal crossbred sons.     

Genotype by environment interaction for livability of dairy calves from first parity cows

Death of calves around parturition is a matter of concern for dairy farmers. Relatively high stillbirth rates and unfavourable trends have been reported for Holstein heifers in the Netherlands and several other countries. In our study, we investigated herd differences, genetic parameters and genotype by environment interaction for heifer calf livability. A large dataset with data from calvings between 1993 and 2012 of Dutch dairy farms was used. There were considerable differences between herds in livability of calves from heifers, with averages ranging from 74% to 95%. Both herds with relatively high and low averages showed the same negative trend between 1993 and 2012, with largest declines in herds with the lowest averages. We found that heritability and genetic variation of first parity livability were substantially larger in herd environments where the likelihood of stillbirth was high v. environments where stillbirth was at a low level. The genetic correlations between herd environment levels were all very close to unity, indicating that ranking of sires was similar for all environments. However, for herds with a relatively high stillbirth incidence selecting sires with favourable breeding values is expected to be twice as profitable as in herds with a relatively low stillbirth incidence.     

Embryo survival in dairy cows managed under pastoral conditions

Efficient pasture-based milk production systems require a compact calving pattern aligned to the onset of the grazing season, a 365-day calving interval and low culling rates for infertility. Achievement of these targets requires high herd reproductive performance. While high genetic merit Holstein cows produce more milk in grass-based systems their fertility is compromised. Management of the modern high genetic merit Holstein dairy cow presents a major challenge in pasture-based systems of production. It appears that the extent of early embryo loss is greater (up to 20% points greater) in the modern high-producing dairy cow and that a much higher proportion of the embryos die before day 7 following insemination in contrast to heifers and lower yielding cows. About 7-8% of pregnancies are lost between days 30 and 90 of gestation with no evidence that loss rate is related to cow genetic merit, parity or level of production. Systemic concentrations of progesterone during both the cycle preceding and following insemination affect embryo survival rate with evidence that too low or indeed too high a concentration of progesterone been negatively associated with embryo survival rate. Peripheral concentrations of both progesterone and oestradiol are lowered by increased plane of feed intake due to increased metabolic clearance rate of the steroids, which is related to liver blood flow. It appears that high producing dairy cows have an increased risk of embryo death as a result of lowered peripheral concentrations of progesterone as a consequence of increased hepatic metabolism of progesterone. Uterine expression of mRNA for progesterone receptor, oestradiol receptor and retinol binding protein mRNA appears to be sensitive to changes in peripheral concentrations of progesterone during the first week after AI. It would appear that energy balance and dry matter intake during the 4 weeks, immediately after calving are critically important in determining conception rate when cows are inseminated at 70-100 days post-calving. Concentrate supplementation of cows at pasture during the breeding period has minimal affects on conception rates though sudden reduction in dietary intake should be avoided. For pasture-based systems of milk production more balanced breeding strategies, with greater emphasis on fertility and feed intake must be developed.     

Higher non-return rate associated with Mycobacterium avium subspecies paratuberculosis infection at early stage in Holstein dairy cows

The effects of infection by Mycobacterium avium paratuberculosis (Map) on dairy cows are poorly documented and quite controversial. This retrospective study aimed at quantifying the variation in non-return to service of Holstein dairy cows according to their Map-infection status. Three different statuses were defined based on both individual and herd tests results: ELISA positive cow, all tests negative cow in a negative herd and all tests negative cow in a positive herd. Whatever the age at Map testing, the status was attributed to a cow from its first lactation onwards. Non-return to service was determined at 200 days after first and second services. The study was performed from 1999 to 2007 on 185,950 AI from 48,914 cows in early stage of the infection in 1069 herds by logistic regression controlling for known factors influencing non-return rate. Non-return rate was higher for infected cows compared to negative cows from negative herds (RR of 1.10 or +3.9 points of % of non-return rate). The effect was significant for parities 1 and 2 (RR of 1.11 and 1.12, respectively) but not for higher ones. This effect was lower when comparing positive cows to negative cows in the same herds but relative risks were still above 1. The hypothesis that the effect of Map on non-return depends upon the stage of infection is formulated.     

Factors potentially affecting fertility of lactating dairy cow recipients

Objectives of this study were to evaluate factors that could affect pregnancy rate after embryo transfer (ET) in lactating dairy cow recipients. The trial was conducted at a dairy farm located in Descalvado, SP, Brazil from October 2003 to September 2004. From 1037 cows with CL that were treated with an injection of PGF2alpha, 43.3% were detected in heat; 263 were previously assigned at day of PGF2alpha injection for AI and 186 for ET. Ovulation rate was 85.7% (385/449). Pregnancy rate for cows with CL for AI and embryo transfer recipients were 36.5% (84/230) and 58.7% (91/155) at day 25 and 33.0% (76/230) and 45.8% (71/155) at day 46, respectively. Embryonic loss were 9.5% (8/84) for the AI group and 21.9% (20/91) for the ET group. Average milk production was 31.4 L/day/cow. Average daily milk production from 7 days before PGF2alpha injection to 7 days after ET tended (P < 0.10) to influence pregnancy rate on days 25 and 46. Average daily milk production from the day of embryo transfer to 7 days after influenced embryonic loss (P < 0.05). Cows with higher milk production had lower probability of pregnancy and higher probability of embryonic loss. Cows with higher days in milk had higher probability of pregnancy. Cows with higher rectal body temperature had lower probability of pregnancy and higher probability of embryonic loss. The influence of high milk yield and body temperature on fertility in lactating dairy cow recipients suggests that these effects can occur also after embryo reaches the blastocyst stage.     

Comparison of reproductive performance by artificial insemination versus natural service sires in California dairies

This study compared the calving to conception intervals for cows in AI pens with cows exposed to natural service sires, controlling for milk production, mastitis occurrence, parity and calving month effects. Records from 10 western United States dairy herds (mean herd size = 2058 cows) were evaluated retrospectively over an 18-month period. Eight bull breeding analysis cohorts were created (the first cohort 0-50 days in milk and the remaining cohorts at 25 days in milk intervals through 226 days). The cohorts contained non-pregnant cows that were first moved into bullpens during the described cohort period. Equal numbers of non-pregnant cows only exposed to AI during the cohort period were randomly selected from the pool of eligible non-pregnant cows. An AI cow was used only once in the data analysis, but was included in a bull breeding cohort at a later date if she remained non-pregnant and was transferred to a bullpen. Univariate and multivariate survival analysis was used to compare the calving to conception intervals. Cows in AI groups had higher hazard rates for pregnancy across all cohorts. Parity and milk production were significantly associated with risk for pregnancy. In herds that practice a mixture of AI and bull breeding, overall herd reproductive performance might be improved by allowing cows more opportunities at AI prior to moving them into clean-up bullpens.     

Abnormal offspring following in vitro production of bovine preimplantation embryos: a field study

Data on 944 calves from 2228 in vitro-produced (IVP) bovine preimplantation embryos were compared with data on 2787 AI calves born in the same herds in 1995. Bovine preimplantation embryos were produced in vitro following ovum pick up (OPU) from donor cows and pregnant heifers in an open nucleus breeding program. After 7 d of in vitro culture on a BRL cell monolayer in the presence of 10% FCS, frozen-thawed expanded blastocysts and fresh morulae to expanded blastocysts were transferred into recipient heifers and cows at 119 contracted farms throughout the Netherlands. The pregnancy rate, as confirmed by palpation per rectum between 90 and 150 d after transfer was 43.5% for both fresh and frozen embryos. Data on IVP and AI calves were registered by the farmers. The percentage of calves with a congenital malformation and the percentage of male calves were related to the total number of calves born. Gestation length, birth weight (measured by a balance), perinatal mortality and ease of calving were analyzed in a subdataset (699 IVP and 2543 AI calves, respectively) by a comparative analysis of variance (ANOVA). The ANOVA model included herd, month of calving, sire nested within AI or IVP, parity and breed of the inseminated cow/embryo recipient, sex of calf, type of calf (AI or IVP) and two-way interactions between type of calf and sex, parity and breed. The percentage of calves with congenital malformations was 3.2% and 0.7% for IVP and AI calves, respectively. An increased incidence of hydro-allantois and abnormal spinal cords and limbs was observed in IVP calves. The percentage of male calves was significantly different between IVP and AI, 55.5% and 48.9%, respectively (Chi-square, 1 degree of freedom, P < 0.05). On the average, IVP calves showed a significant increase of birth weight by 10% (4-5 kg), a 3-d longer gestation period, 2.4% more perinatal mortality and a more difficult calving process compared to AI calves (P < 0.05). From these results it is concluded that calves produced by IVP deviate significantly from calves produced by AI.     

Danish A.I. field data with sexed semen

The objective of this study was to compare conception rates, non-return rates and sex ratios of sexed and conventional semen from the same sires in commercial dairy herds in Denmark. The semen was produced from three bulls from each of the three major dairy breeds in Denmark: Holstein, Jersey and Danish Red Dairy Breed (nine bulls total), in order to answer questions on breeds differences in field results. AI was performed by trained technicians using a minimum of 150 doses of sorted sperm and 50 control doses from each bull. During the trial, a total of 2087 doses were used in 63 herds.The trial showed that the conception rate using sorted semen was 5% points lower than with conventional doses for Danish Reds, 7% points for Jerseys, and 12% points for Holsteins. Translating this into non-return rate revealed differences of 10-20% points among bulls. These differences are thought to be a good indicator of what to expect from commercial use of sexed semen.The sex ratios varied from 89% to 93% female calves among breeds, which on average is consistent with the theoretical average sex ratio of 93% females considering the low number of inseminations.     

Prevalence of, and risk factors associated with, perinatal calf mortality in pasture-based Holstein-Friesian cows

Recent publications indicate that the prevalence of perinatal mortality has increased in some dairy industries and an increased proportion of this loss is not associated with the traditional risk factors for perinatal mortality. The objectives of this study were to establish the prevalence of perinatal mortality (calf death within 24 h of calving) in Irish dairy herds and to determine the current significance of putative risk factors in pasture-based management systems. A total of 182 026 records of full-term calvings from Holstein-Friesian dams served by artificial insemination (AI) sires of seven breeds in herds of 20 calvings or more per year were available from the Irish national breeding database over 4 years (2002 to 2005). The prevalence of perinatal mortality was 4.29% (7.7% in primiparae and 3.5% in pluriparae). The likelihood of perinatal mortality increased between 2002 and 2005 and was greatest in June and in winter. There was an interaction (P < 0.001) between the effect of calving assistance and parity with the effect of dystocia on perinatal mortality being greater in primiparae. The odds of perinatal mortality were greater in male (OR = 1.12; P < 0.001) and in twin calves (OR = 5.70-13.36; P < 0.001) and in dams that had perinatal mortality at the previous calving (OR = 4.21; P < 0.001). The logit of the probability of perinatal mortality increased by 0.099 per unit increase in sire predicted transmitting ability (PTA) for direct perinatal mortality. The probability of perinatal mortality increased at an increasing rate in primiparae as animals calved at a younger age relative to the median age at first calving. The only herd-level factor examined, herd size did not affect the odds of perinatal mortality. These data indicate that the prevalence of perinatal mortality in this cattle population is similar to that in other pasture-based dairy systems worldwide. The putative exposures and attributes traditionally associated with perinatal mortality were associated with perinatal mortality in this pasture-based dairy cow population. The practical implication of these results is that as many of the significant risk factors are largely not under management control (year of calving, month of calving, twin calving, primiparity, previous perinatal mortality and foetal gender), herd owners must focus on the significant determinants under their control (age at first calving, sire genetic merit for direct perinatal mortality and both the extent of calving supervision and the degree of assistance), in order to reduce the prevalence of perinatal mortality and improve perinatal welfare.     

Farm characteristics related to on-farm cow mortality in dairy herds: a questionnaire study

Dairy cow mortality is an important animal welfare issue that also causes financial losses. The objective of this study was to identify farm characteristics and herd management practices associated with high on-farm cow mortality in Swedish dairy herds. A postal questionnaire was sent to farmers that had either high or low mortality rates for 3 consecutive years. The questionnaire consisted of five sections: ‘About the farm’, ‘Milking and housing’, ‘Feeding’, ‘Routines’ and ‘Lame and sick cows’. A total of 145 questionnaires were returned (response rate=33%). Ten of the 77 characteristics investigated met the inclusion criteria for multivariable analysis. The final logistic regression model included: herd size, breed, use of natural service bull, bedding improvement frequency and pasture system. Herds with Swedish Holstein as the predominant breed (odds ratio (OR) 22.9, 95% confidence interval (CI) 5.2 to 101.8) or with mixed breeds (OR 5.5, 95% CI 1.7 to 17.5) had a greater risk of being high mortality herds than herds that were predominantly Swedish Red (OR 1). Herds larger than 100 cows (OR 19.6, 95% CI 3.5 to 110.4) and herds with 50 to 99 cows (OR 13.8, 95% CI 3.2 to 60.6) had greater risk of mortality than herds numbering 35 to 50 cows (OR 1). Being a high mortality herd was also associated with having cows on exercise lots during the summer season (OR 3.6, 95% CI 1.3 to 9.9) compared with on pasture. A missing answer on the question of bedding improvement frequency was associated with high mortality herds. Overall, this study suggests that characteristics that are related to intensification of the dairy industry are also associated with high on-farm mortality of dairy cows.     

Initial insights on the performances and management of dairy cattle herds combining two breeds with contrasting features

Finding ways of increasing animal production with low external inputs and without compromising reproductive performances is a key issue of livestock systems sustainability. One way is to take advantage of the diversity and interactions among components within livestock systems. Among studies that investigate the influence of differences in animals’ individual abilities in a herd, few focus on combinations of cow breeds with contrasting features in dairy cattle herds. This study aimed to analyse the performances and management of such multi-breed dairy cattle herds. These herds were composed of two types of dairy breeds: ‘specialist’ (Holstein) and ‘generalist’ (e.g. Montbeliarde, Simmental, etc.). Based on recorded milk data in southern French region, we performed ANOVA: (i) to compare the performances of dairy herds according to breed-type composition: multi-breed, single specialist breed or single generalist breed and (ii) to test the difference of milk performances of specialist and generalist breed cows (n = 10 682) per multi-breed dairy herd within a sample of 22 farms. The sampled farmers were also interviewed to characterise herd management through multivariate analysis. Multi-breed dairy herds had a better trade-off among milk yield, milk fat and protein contents, herd reproduction and concentrate-conversion efficiency than single-breed herds. Conversely, they did not offer advantages in terms of milk prices and udder health. Compared to specialist dairy herds, they produce less milk with the same concentrate-conversion efficiency but have better reproductive performances. Compared to generalist dairy herds, they produce more milk with better concentrate-conversion efficiency but have worse reproductive performances. Within herds, specialist and generalist breed cows significantly differed in milk performances, showing their complementarity. The former produced more milk for a longer lactation length while the latter produced milk with higher protein and fat contents and had a slightly longer lactation rank. Our results also focus on the farmers’ management of multi-breed dairy herds underlying herd performances. Three strategies of management were identified and structured along two main axes. The first differentiates farmers according to their animal-selection practices in relation with their objectives of production: adapting animal to produce milk with low-feeding inputs v. focussing on milk yield trait to intensify milk production. The second refers to the purpose farmers give to multi-breed dairy herds: milk v. milk/meat production. These initial insights on the performances and management of multi-breed dairy herds contribute to better understanding the functioning of ruminant livestock systems based on individual variability.     

Maximum likelihood estimation of the parameters of the prior distributions of three variables that strongly influence reproductive performance in cows

Ovulation detection rate, pregnancy rate, and embryo loss rate greatly affect the reproductive performance of cows. A previous model described the separate effects of these variables on the resulting calving patterns and assumed that the variables have the same value for all cows belonging to the same herd. This is not a realistic biological assumption, so the beta distribution is used to introduce "between-cow" variation in the three variables. Two approaches are used to find maximum likelihood estimates of the parameters of these prior beta distributions. The first considers sequences of ovulations, artificial inseminations, and pregnancies, separately. For both ovulation detection rate and pregnancy rate this approach considers the number of "successes" of each event for a particular cow (e.g., in the case of an ovulation, a success is a detection), and conditions on the total number of occurrences of that event in the cow, so that beta-binomial distributions are considered. However, for embryo loss rate the number of pregnancies required until a particular cow calves is considered, so that a beta-geometric distribution results. If the cow is removed before she calves, a censored sequence will result. The second approach considers the sequences of ovulations, artificial inseminations, pregnancies, and embryo losses, together, which will stop only when the cow calves. Otherwise, if she is removed before that time, a censored sequence will result. In this case, a joint distribution, with three independent prior beta distributions, is considered. The results of the analysis of data from 22 herds are discussed.     

Breed of cow and herd productivity affect milk nutrient recovery in curd,and cheese yield,efficiency and daily production

Little is known about cheese-making efficiency at the individual cow level, so our objective was to study the effects of herd productivity, individual herd within productivity class and breed of cow within herd by producing, then analyzing, 508 model cheeses from the milk of 508 cows of six different breeds reared in 41 multi-breed herds classified into two productivity classes (high v. low). For each cow we obtained six milk composition traits; four milk nutrient (fat, protein, solids and energy) recovery traits (REC) in curd; three actual % cheese yield traits (%CY); two theoretical %CYs (fresh cheese and cheese solids) calculated from milk composition; two overall cheese-making efficiencies (% ratio of actual to theoretical %CYs); daily milk yield (dMY); and three actual daily cheese yield traits (dCY). The aforementioned phenotypes were analyzed using a mixed model which included the fixed effects of herd productivity, parity, days in milk (DIM) and breed; the random effects were the water bath, vat, herd and residual. Cows reared in high-productivity herds yielded more milk with higher nutrient contents and more cheese per day, had greater theoretical %CY, and lower cheese-making efficiency than low-productivity herds, but there were no differences between them in terms of REC traits. Individual herd within productivity class was an intermediate source of total variation in REC, %CY and efficiency traits (10.0% to 17.2%), and a major source of variation in milk yield and dCY traits (43.1% to 46.3%). Parity of cows was an important source of variation for productivity traits, whereas DIM affected almost all traits. Breed within herd greatly affected all traits. Holsteins produced more milk, but Brown Swiss cows produced milk with higher actual and theoretical %CYs and cheese-making efficiency, so that the two large-framed breeds had the same dCY. Compared with the two large-framed breeds, the small Jersey cows produced much less milk, but with greater actual and theoretical %CYs, similar efficiencies and a slightly lower dCY. Compared with the average of the specialized dairy breeds, the three dual-purpose breeds (Simmental and the local Rendena and Alpine Grey) had, on average, similar dMY, lower actual and theoretical %CY, similar fat and protein REC, and slightly greater cheese-making efficiency.     

Antimicrobial use in organic and conventional dairy herds

Use of antimicrobials for food-producing animals is a major public concern due to the risk of antimicrobial resistance. Although dairy production has a relatively low usage of antimicrobials, the potential for further reduction should be explored. The objective of the study was to estimate the current differences in antimicrobial use in Danish organic and conventional dairy herds and to describe the differences between them. Based on data from three different sources, 2604 herds (306 organic and 2298 conventional) were identified for the study. These herds had been either organic or conventional for the entire period from 2015 to 2018. Antimicrobial use was calculated as the treatment incidence in Animal Daily Doses (ADDs)/100 animals/day for three age groups: adult cattle, young stock and calves. For adult cattle, the ratio of median treatment incidence between conventional and organic production ranged from 2.8 : 1 to 3.4 : 1, depending on the specific year. For cows, 25% of the organic herds had a higher treatment incidence than the 25% of conventional herds with the lowest treatment incidence. Antimicrobial use for young stock was low and at a similar level in both the organic and conventional production systems. For calves, the median treatment incidence was 1.2 times higher in conventional herds and 1.6 times higher for the 75th percentile. Analyses of treatment incidence in adult cattle showed an overall decrease from 2015 to 2018 in both organic and conventional herds. The decrease was greater for the conventional herds (0.12 ADD/100 animals/day) compared to the organic herds (0.04 ADD/100 animals/day) over the 4-year period. In addition, herd size was an important risk factor for treatment incidence in conventional herds, increasing by 0.07 ADD/100 animals/day per 100 cows, whereas herd size had a minor influence on the treatment incidence in organic herds. The results of this study demonstrate the large variation in antimicrobial use within both organic and conventional herds, suggesting that further reduction is possible. Furthermore, herd size appears to be a risk factor in conventional herds but not in organic herds – an aspect that should be studied in more detail.