Successive Calvings Research Articles

Genetic parameters for reproductive traits in the Italian Mediterranean buffalo using milk yield as a correlated trait

Until now, the genetic evaluation of the Italian Mediterranean Buffalo has been mainly focused on production traits. However, female fertility affects the efficiency of the dairy industry as it is essential to maintain the profitability of dairy farms. Indeed, the estimation of its genetic component is crucial for its improvement. In this study, 3 measures of buffalo's fertility were analyzed: the age at first calving (AFC), the interval between first and second calving (CI1), and the interval between second and successive calvings (CI2_12). Milk yield at 270 d (MY270) was used as a correlated trait. First, genetic parameters were estimated using 7,915 buffalo cows with first calving from 1991 to 2018, then breeding values were calculated from 236,087 buffalo cows. Genetic parameters were estimated by Bayesian inference fitting a multiple-trait animal model using the GIBBS1F90 program while BLUPF90 was used for estimation of breeding value. The heritability and repeatability estimates of fertility traits were low. The genetic correlations among fertility traits ranged from 0.10 (AFC-CI1) to 0.92 (CI1-CI2_12). Genetic correlation between MY270 and fertility traits was unfavorable, ranging from 0.23 to 0.48. The results from this study can be used as a basis for the future genetic improvement of fertility traits in the Italian Mediterranean Buffaloes.

Individual‐based assessment of post‐translocation fitness of ungulates: Lessons from the critically endangered Derby eland conservation programme

AbstractTranslocations have become an essential tool in animal conservation for establishing and maintaining viable populations. Yet, the viability of a population is implicitly based on the individual fitness, that is on the survival and reproduction of individuals. Individual‐based assessments of post‐translocation fitness are challenging in the wild while conservation breeding programs may provide vital insights. Long‐term breeding records of semi‐captive (fenced) small population of the Western Derby eland (Taurotragus derbianus derbianus) running in two fenced reserves in Senegal present a case study. This study shows that transport distance and the individual's age at translocation influence animal post‐translocation survival rates and individual reproductive performance. The most critical period for the antelope's post‐translocation survival was the first 2 years following the event, with higher mortalities reported after long‐distance transport in an ecologically novel environment. The first successful calving of translocated females was postponed by 1 year, but the life‐long reproductive performance was not affected. However, higher calf survival in a habitat similar to that in the wild suggests a non‐negligible effect of the habitat on individual fitness, thus crucial to conservation decisions on translocating threatened species.

Hormonal regulation of the concentration of glucose and its derivatives in the blood of dairy cows during the transit period

In dairy cows, metabolic disorders are mainly found in the last weeks of the dry period and the first weeks after calving (transit period). Therefore, the purpose of this study was to investigate the hormonal regulation of the concentration of glucose and its derivatives in the blood of dairy cows during the transit period. The study was conducted on cows of 2-4 lactations, with a capacity of 7.8-8.2 thousand kg of milk for previous lactation. Blood for research was taken from cows 7-10 days before calving and Days 2-4, Days 10-14, and Days 30-40 after calving. The concentration of glucose in blood plasma was determined by the glucose oxidase method, pyruvate − by the modified Umbright method, lactate – by reaction with paraoxydyphenyl, and hormone content – by enzyme-linked immunosorbent assay. It was established that high-performance dairy cows during the transit period experience substantial changes in carbohydrate metabolism and the functional state of organs and systems, which are aimed at ensuring high productivity. Thus, hypoglycaemia is found in cows within two weeks after calving. At the same time, with a decrease in the concentration of glucose in the blood plasma of cows, the content of pyruvate and lactate increases, as well as the lactate/pyruvate ratio, which indicates an increase in gluconeogenesis. Negative energy balance and increased gluconeogenesis lead to a decrease in the synthesis of insulin and insulin-like growth factor. Compared to the final dry period, on Days 2-4 of lactation, the concentration of leptin in the blood plasma of cows decreased threefold and stayed at a low level until Day 40 of lactation. Plasma cortisol levels were highest on Days 2-4 and 10-14 of lactation. Intensive cortisol synthesis during the period of energy deficiency increases gluconeogenesis, which is possible due to lipolysis and proteolysis. In the first days after calving, the content of thyroxine and triiodothyronine in the blood plasma of cows decreased. Inhibition of thyroid hormone production is a consequence of the physiological regulatory features of this period. Thus, in highly productive cows during the transit period, attention should be paid to maintaining vital body functions and their well-coordinated endocrine regulation, which will ensure a physiologically balanced metabolic rate, successful calving, high milk productivity, and animal health

Dairy productivity of Yenisei red-motley cows as a function of growth rate and age of fertile insemination

The main task in dairy farming is the proper breeding of heifers to realise their genetic potential further. The research aims to study the impact of the growth rate of heifers and heifers of Yenisei type of red-motley breed on their subsequent dairy productivity. The research was conducted in the breeding plant of Solgon JSC of the Uzhur district, Krasnoyarsk Territory. The heifer population (1156 heifers) was divided into eight groups according to the age of fertile insemination. The first three groups were fast-growing animals (10-14 months of fertile insemination), the remaining five groups were slow-growing animals (15 months of fertile insemination or older). The authors chose the following indicators to study: live weight, average daily live weight gain, age of first successful insemination and first calving, and milk productivity of cows in 305 days of the first lactation. Fast-growing heifers were found to outperform slow-growing heifers in terms of growth rate. The live weight of fast-growing heifers was 102 grams greater, or 11.6% than that of slow-growing heifers from birth to first fertile insemination. The live weight of fast-growing heifers was 83 grams or 11.3%, more outstanding from birth to first calving. A comparative analysis of the milk production of fast- and slow-growing animals showed no significant difference between the groups on average. However, the difference in milk yield and milk fat and protein between the individual groups was statistically significant. Studies have confirmed that heifers of the Yenisei type can be inseminated quite successfully at an earlier age (12-14 months). Heifers of this type enter the production group more quickly and cost less to raise (by 4,742 roubles or 11.9%), which has an impact on profit (by 5,844 roubles or 30.2%) and profitability levels (by four percentage points or 40%).

Evaluation of milk urea concentrations and their relationship with milk production, rumen degradable proteins imbalance, and cow’s fertility in a dairy farm in Haouz, central Morocco

The effect of some factors on relationships between milk urea concentrations, milk production, negative OEB diet and fertility of 74 cows were analyzed. Diets were calculated using the French PDI system and SPSS 20 package was used for statistical analysis. Milk urea concentrations ranged from 31.7± 1.6 mg/dl in low-producing cows (17.3 ± 2.3 kg milk) to 32.3 ±2.0 mg/dl in high-producing cows (25.1 ± 4.4 kg milk). The increase of milk urea concentrations was found to increase interval between calving and conception (p less than 0.00), number of inseminations per conception (p less than 0.01) and interval between two successive calvings (p less than 0.00). Increasing of urea in milk in relation with feeding diets characterized by negative OEB might decrease milk production and fertility in dairy herd. Therefore, dairy breeders may find it advantageous to monitor milk urea, which could help to improve nutritional status and cow’s fertility.

Development of enzyme-linked immunosorbent assay for early pregnancy diagnosis in cattle

The prerequisite for enhancing reproductive efficacy and successful calving is an early and accurate diagnosis of pregnancy. A highly sensitive enzyme-linked immunosorbent assay (ELISA) utilizing the second antibody coating technique and the horseradish peroxidase conjugate as a label for the determination of Interferon-stimulated protein, 15 kDa (ISG15) in dairy cows was developed. To validate a neutrophil lysate based ELISA for early pregnancy diagnosis, blood samples from healthy multiparous Karan Fries (KF) cows were collected on day 0 (day of AI), 10, 14, 16 and 21 post artificial insemination. The pregnancy and non-pregnancy in cows were confirmed by plasma progesterone assay, ultrasonography and per rectal palpation. The detection range of the assay was 0.312 to 25 ng/ml with a sensitivity of 0.13 ng/ml. The inter-assay and intra-assay coefficient of variation was 12.1% and 10.1%, respectively. The parallelism for measured and expected concentrations had an r2 value of 0.90 and 0.93, respectively. It was observed that ISG15 concentration was greater (P < 0.01) in pregnant as compared to non-pregnant cows, the greatest being 9.36 ± 0.50 ng/ml on day 16 in pregnant cows. With the use of immunocytochemistry, there was a positive staining for ISG15 with greater staining in the neutrophils of day 16 pregnant cows. The study reveals that ISG15 protein in a neutrophil lysate can be utilized as a biomarker for early pregnancy diagnosis in cows.

Pregnancy outcomes based on milk pregnancy-associated glycoprotein levels

Timely diagnosis of pregnancy and pregnancy losses is economically important. A commercially available pregnancy-associated glycoprotein (PAG) milk assay (IDEXX Laboratories, Inc.) is offered through routine Dairy Herd Improvement (DHI) testing for diagnosis of pregnancy. The objective of this observational study was to describe the relationship between PAG at various stages of gestation and the likelihood of successful calving. The hypothesis was that higher PAG levels would be associated with successful calving.

Meta-assembly of genomic regions and variants associated with female reproductive efficiency in cattle

Decline in fertility in last few decades, especially in high milk producing dairy cows, is a major concern in many countries. Fertility is a compound trait of many events leading up to successful calving and subsequent lactation. Fertility traits in cattle have relatively low heritability. Recently a number of studies have searched for genomic regions and variants associated with various reproduction traits in cattle. We constructed a systematic meta-assembly of 35 QTL studies and separately for 23 genome-wide association studies (GWAS) related to female fertility in cattle representing over 101,000 genotyped individuals. We separately compiled and discussed additional candidate gene studies, fine-mapping studies, selection signatures and other novel potential biomarkers associated with female reproduction in cattle. Despite individual studies being low powered, inherent low heritability of fertility traits and low success of genomic selection for fertility traits, a substantial number of strong signals, causative mutations and biomarkers for fertility have been identified throughout the genome. A number of embryonic lethal mutations and haplotypes have been identified using novel approaches. These markers can be used for population screening, genomic-assisted mating plans, and can be incorporated in a marker assisted framework for genetic improvement in the fertility. The studies investigating the role of epigenomic markers are in the early stages, and may provide important biomarkers in near future. Novel approaches linking metabolomic and epigenetic markers, and high resolution genome content to high quality phenotypes will assist in our understanding of the genetic architecture of complex traits underlying fertility in cattle.

GENETIC AND PHENOTYPIC PARAMETERS OF MILK YIELD AND REPRODUCTIVE PERFORMANCE IN THE FIRST THREE LACTATIONS OF EGYPTIAN BUFFALO

The objective of this work was to investigate early selection based on the first lactation to improve milk yield in the first three lactations. A total of 1911 lactation records each for milk yield, lactation length, age at first calving and average interval between successive calvings, representing 637 buffalo cows, daughters of 123 sires and 519 dams, were analyzed by fitting a multiple-trait animal model using REML procedure. The model included herd and year-season of birth as fixed effects and animal as random effect. The results revealed that the fixed effect of herd contributed significantly to variation in all studied traits except for age at first calving, while year-season of birth significantly affected milk per day/lactation, first lactation length, age at first calving and average interval between successive calvings. Heritability estimates for milk yield, cumulative milk yield, milk per day/lactation and first lactation length varied from 0.13 to 0.27. Heritability estimates for age at first calving and average interval between successive calvings were 0.11 and 0.07, respectively. Genetic and phenotypic correlations were high and positive for milk yield, cumulative milk yield, milk per day/lactation and first lactation length. While, it was moderate to low for these traits with both age at first calving and average interval between successive calvings. Results indicated that early genetic selection of milk yield for the first three lactations based on the first one is possible through a selection scheme in the Egyptian buffalo.

Performance of steer progeny of sires differing in genetic potential for fatness and meat yield following postweaning growth at different rates. 2. Carcass traits

The steer progeny of sires genetically diverse for fatness and meat yield were grown at different rates from weaning to feedlot entry and effects on growth, carcass and meat-quality traits were examined. The present paper, the second of a series, reports the effects of genetic and growth treatments on carcass traits. A total of 43 sires, within three ‘carcass class’ categories, defined as high potential for meat yield, marbling or both traits, was used. Where available, estimated breeding values for the carcass traits of retail beef yield (RBY%) and intramuscular fat (IMF%) were used in selection of the sires, which were drawn from Angus, Charolais, Limousin, Black Wagyu and Red Wagyu breeds, to provide a range of carcass sire types across the three carcass classes. Steer progeny of Hereford dams were grown at either conventional (slow: ~0.5 kg/day) or accelerated (fast: ~0.7 kg/day) rates from weaning to feedlot entry weight, with group means of ~400 kg. Accelerated and conventionally grown groups from successive calvings were managed to enter the feedlot at similar mean feedlot entry weights at the same time for the 100-day finish under identical conditions. Faster-backgrounded groups had greater fat levels in the carcass than did slower-backgrounded groups. Dressing percentages and fat colour were unaffected by growth treatment, whereas differences in ossification score and meat colour were explained by age at slaughter. There were significant effects of sire type for virtually all carcass traits measured in the progeny. Differences in hot standard carcass weight showed a clear advantage to European types, with variable outcomes for the Angus and Wagyu progeny. Sire selection by estimated breeding values (within the Angus breed) for yield and/or fat traits resulted in expected differences in the progeny for those traits. There were large differences in both meat yield and fatness among the types of greatest divergence in genetic potential for those traits, with the Black Wagyu and the Angus IMF clearly superior for IMF%, and the European types for RBY%. The Angus IMF progeny performed as well as that of the Black Wagyu for all fatness traits. Differences in RBY% among types were generally reflected by similar differences in eye muscle area. Results here provide guidelines for selecting sire types to target carcass traits for specific markets. The absence of interactions between growth and genetic treatments ensures that consistent responses can be expected across varying management and production systems.

Erratum to: Performance of steer progeny of sires differing in genetic potential for fatness and meat yield following postweaning growth at different rates. 2. Carcass traits

The steer progeny of sires genetically diverse for fatness and meat yield were grown at different rates from weaning to feedlot entry and effects on growth, carcass and meat-quality traits were examined. The present paper, the second of a series, reports the effects of genetic and growth treatments on carcass traits. A total of 43 sires, within three 'carcass class' categories, defined as high potential for meat yield, marbling or both traits, was used. Where available, estimated breeding values for the carcass traits of retail beef yield (RBY%) and intramuscular fat (IMF%) were used in selection of the sires, which were drawn from Angus, Charolais, Limousin, Black Wagyu and Red Wagyu breeds, to provide a range of carcass sire types across the three carcass classes. Steer progeny of Hereford dams were grown at either conventional (slow: ~0.5 kg/day) or accelerated (fast: ~0.7 kg/day) rates from weaning to feedlot entry weight, with group means of ~400 kg. Accelerated and conventionally grown groups from successive calvings were managed to enter the feedlot at similar mean feedlot entry weights at the same time for the 100-day finish under identical conditions. Faster-backgrounded groups had greater fat levels in the carcass than did slower-backgrounded groups. Dressing percentages and fat colour were unaffected by growth treatment, whereas differences in ossification score and meat colour were explained by age at slaughter. There were significant effects of sire type for virtually all carcass traits measured in the progeny. Differences in hot standard carcass weight showed a clear advantage to European types, with variable outcomes for the Angus and Wagyu progeny. Sire selection by estimated breeding values (within the Angus breed) for yield and/or fat traits resulted in expected differences in the progeny for those traits. There were large differences in both meat yield and fatness among the types of greatest divergence in genetic potential for those traits, with the Black Wagyu and the Angus IMF clearly superior for IMF%, and the European types for RBY%. The Angus IMF progeny performed as well as that of the Black Wagyu for all fatness traits. Differences in RBY% among types were generally reflected by similar differences in eye muscle area. Results here provide guidelines for selecting sire types to target carcass traits for specific markets. The absence of interactions between growth and genetic treatments ensures that consistent responses can be expected across varying management and production systems.

Performance of steer progeny of sires differing in genetic potential for fatness and meat yield following post-weaning growth at different rates. 1. Growth and live-animal composition

The present experiment, ‘Regional Combinations’, examined growth, and carcass- and meat-quality traits in the progeny of sires genetically diverse for fatness and meat yield when grown at different rates from weaning to feedlot entry. The present paper is the first of several papers describing results from the New South Wales site, one of four in the project. It reports the effects on growth and body composition of steers during backgrounding and feedlot finishing phases. A total of 43 sires within three carcass-class categories, defined as high potential for meat yield, for marbling or for both traits, was used, based on estimated breeding values for retail beef yield and intramuscular fat. Sires were drawn from Angus, Charolais, Limousin, Black Wagyu and Red Wagyu breeds, providing a range of carcass sire types across the three carcass classes. Matings were by artificial insemination to Hereford dams from a single herd. Steer progeny were grown at conventional (slow: ~0.5 kg/day) or accelerated (fast: ~0.7 kg/day) rates from weaning to feedlot entry weight, targeting group means of 400 kg. Accelerated and conventionally grown groups from successive calvings entered the feedlot at similar entry liveweights at the same time, then having identical management during the 100-day finishing phase before slaughter. Within finishing cohorts, fast backgrounding growth resulted in increased subcutaneous fatness at feedlot entry in steers of all carcass types. Slow growth during backgrounding resulted in faster (compensatory) growth in the feedlot in all classes and sire types. This increased the deposition of fat in slow-backgrounded steers compared with that in fast-backgrounded steers during feedlotting, and thus reduced the difference between the groups in P8 and rib fat at feedlot exit. However, there did appear to be an advantage in the level of compensation in the feedlot in favour of those sire types with a genetic propensity for faster growth. Backgrounding growth rate affected body composition and the rate of weight gain during finishing. Faster growth produced more subcutaneous fat during both backgrounding and finishing. Steer progeny groups clearly showed the expected responses in growth and body composition, on the basis of the genetic potential of their sires.

A New Perspective on Management of Reproduction in Dairy Cows: the Need for Detailed Metabolic Information, an Improved Selection Index and Extended Lactation

For lactating dairy cows, we need management tools, that are "clean, green and ethical", cost-effective and easy to use. Specific tools are needed for artificial insemination (AI) after oestrus detection within a few months of calving, and for managing the complex nutritional requirements of cows between successive calvings. Assessment of energy deficit by measurement of body condition score (BCS) has been useful in the past but we now need more sophisticated ways to measure the relationship between adipose tissue and fertility. For this reason, we have focused our attention on the cells of the adipose tissue, the adipocytes, and the role of the hormone that they produce, leptin. This hormone affects pulsatile LH release and, in dairy cows, it seems to be linked to the first postpartum ovulation. Adipocytes are always sensing energy status and they control leptin secretion dynamically, so blood leptin concentrations can change acutely, even when there is no detectable change in BCS. Leptin secretion seems to be determined by the secretory activity of each adipocyte as well as the total mass of adipocytes in the body of the animal (as measured by BCS). The strong relationship between BCS, leptin concentration and reproductive function in dairy cows suggests that we should reconsider the interval of the recovery from prepartum and postpartum damages, the need for high milk yields at the last lactation causing the dry-off stress and the subsequent troubles. We should also re-assess the current drive to reduce calving interval because milk yields during the early stages of lactation are economically very important but high yields seem to cause several metabolic and reproductive disorders in modern dairy cows. In general, the thinking has been that calving interval must be short because short intervals are more profitable. However, if we remember that main product from dairy cows is milk and that a short calving interval is very difficult without reproductive problems, then a longer calving interval might be more sensible and also more profitable. We have example of an extended calving interval in Japan, Supercows which are very rare cows yielding remarkable high milk. Finally, we probably need to improve dairy cows genetically if we are to achieve the goal of "clean, green and ethical" dairy farming. This paper reviews data relevant to these strategies and we conclude that more basic and applied research will be required if we are to find ways to reach that goal.

Comparison of external morphological traits of newborns to inner morphological traits of the dam in the double‐muscled Belgian Blue Beef breed

SummaryIn the double‐muscled (DM) Belgian Blue Beef (BBB) breed, caesarean section (CS) is used as a routine management tool to prevent dystocia. This practice is criticized on animal welfare grounds. With unassisted (natural) births, difficulties arise because of disproportion between the sizes of the newborn and inner pelvic sizes of the dam. In this study external morphological traits of newborns are compared with inner morphological traits of the dam. Results of this study indicate that in the DM‐BBB, CS is the only means to successful calving. Therefore, no calving ease scores are available to select for less dystocia in this breed. Selection for fewer CS must be achieved by focusing on lower birth weight (BW) and decreased muscular conformation at birth, both having a sufficiently high heritability. Simultaneously, pelvic sizes of the dam should be increased. It is very likely that the look of the DM‐BBB will change when selecting for less dystocia.

Body condition in Svalbard reindeer and the use of blood parameters as indicators of condition and fitness

Body condition is an important determinant of ecological fitness but is difficult to measure in field studies of live animals. Live mass and subcutaneous fat are often used as proxies for body condition and related to fitness. We investigated the relationship between blood-chemistry parameters and live mass and back-fat thickness and assessed their usefulness as predictors of ecological fitness in a wild arctic ungulate population, Svalbard reindeer (Rangifer tarandus platyrhynchus). Female reindeer were sampled in late winter between 1995 and 2002 and concentrations of blood parameters were related to subsequent survival and successful calving. There was marked annual variation in all blood parameters, live mass, and back-fat thickness, reflecting variation in weather and food availability. At the individual level, variation in blood-parameter concentrations was not closely related to variation in live mass or back-fat thickness, instead reflecting shorter term nutritional status. Blood parameters could therefore provide useful additional information, enhancing the predictive power of fitness models based on live mass. The urea:creatinine ratio significantly improved adult survival models, while β-hydroxybutyric acid and creatinine concentrations were significant predictors of calving success. The applications for blood parameters in ecological investigations look promising and should be tested more widely in other field studies.

Nutrition-induced changes in blood chemical parameters of pregnant reindeer hinds ( Rangifer tarandus tarandus)

Twenty-four pregnant reindeer hinds ( Rangifer tarandus tarandus) were allocated to three feeding groups during 110 days experiment from January to May. Group 1 was grazing in a 15 km 2 fence, their diet mimicking a good quality winter pasture. Group 2 was fed with lichens. Their energy supply was gradually decreased until it was 30% from the ad libitum amount at the start. Group 3 was fed ad libitum with a pelleted concentrate for reindeer. Lichen fed animals lost 15% of body weight during the experiment. In other groups body weight was either maintained (Group 1) or increased by 18% (Group 3). Serum protein concentration decreased from 77 g/l to 62 g/l in lichen fed animals, accompanied first with a fall in serum urea concentration. When energy supply decreased further, a rise in blood urea occurred. Serum creatinine concentration increased with lichen feeding, and after 2 months it was 61% higher than at the beginning of the experiment. In pellet fed hinds creatinine declined from 190 μmol/l to 143 μmol/l. The birth weight of calves reflected the nutritional status of the groups. The average birth weight was 6.3 kg for calves of pellet fed hinds, 5.9 kg in group with mimicked winter diet and 4.0 kg for lichen fed group. Normal winter diet seems to provide enough energy and protein for the maintenance of body weight and for successful calving. Pellet feeding increased body weight, and had a positive effect on birth weights of calves. On poor winter pasture, supplementary feeding can be useful in prevention of malnutrition and in improving of calving success.

The role of nutrition, body condition and lactation on calving success in muskoxen

Relationships between nutrition, body weight (BW), body condition score (BCS) and fertility were explored in 11 captive female muskoxen between 1988–1994. In 1987, six adult female muskoxen were allocated to high plane (HP) or low plane (LP) nutritional treatments (HP n= 3; LP n= 3), which were maintained year‐round through spring 1995 (HP n= 6; LP n= 5). Treatment group size fluctuated annually. Age, lactation status, calving date and calf birth weight were recorded for each cow. Body weight was measured weekly and BCS measured bi‐weekly throughout the mating season from 1 August to 31 October. Sixty‐one complete observations of BW and BCS in autumn, lactation status and calving success were collected. Body weight and BCS differed significantly (t‐test) with pregnancy (P &lt; 0.001) and nutritional treatment (P &lt; 0.001). A significant logistic regression model was generated for the relationship between BW in October and pregnancy (P &lt; 0.001). When BCS each month was combined with BW in October, BCS in September was the most significant variable (P &lt; 0.001) and the only one to enter the model. Neither lactational status nor year, in combination or alone, was significant. Both BW in autumn (176 kg provides a 50% probability of a female calving the following spring) and BCS (score of six provides a 50% probability of successful calving) can be useful predictors of fertility in muskoxen. The ability of muskoxen to make significant gains in weight and body condition in autumn may represent a nutritional control point regulating reproduction in this species.

Stocking rate, calving season and post-weaning growth effects for Angus cattle on annual pasture

The effects of stocking rate, calving season and post-weaning growth were investigated over 3 years for Angus cattle on annual pastures. Angus cows, mated to Angus bulls for 8 weeks to start calving early summer (ES), early autumn (EA) or early winter (EW), were stocked at 0.6, 0.8 and 1.0 cows/ha and calves/ha until their fourth calving ended. Weaning, at average age 10.5 months, was at the end of October, January or April. Some calves were slaughtered at weaning and others after a year at 1.4 calves/ha. Late autumn-winter pasture growth [2500-3500 kg dry matter (DM)/ha] was below average in 2 of the 3 years of the study, and spring growth did not vary (overall mean 4400 kg DM/ha). Unseasonable pasture growth during late summer-early autumn occurred between weaning in EA and EW for years 2 and 3. Milk consumption was an overall average of 4.8 kg/ca1f.day. The only variation was a higher value in EW in year 2 than in years 1 and 3. Winter calf growth in ES and EA was sometimes affected by year and stocking rate, and overall average spring growth was 1.23, 1.33 and 1.13 kg/calf.day in ES, EA and EW, respectively. Weaning weight occasionally differed with stocking rate in ES and EA, and tended to differ between years in EW in proportion to the level of unseasonable pasture growth. Overall, carcasses tended to be slightly heavier and fatter in ES but otherwise followed the weaning weight patterns. Minimum cow weight tended to vary with stocking rate in years 2 and 3 and overall increased from ES to EW. Maximum weight also differed in these years. Yearly treatment means for average daily weight change during mating were -1.47 to +1.45 kg/cow. Weight gain declined from ES to EW except for reversal of the ES and EA situations in year 3 when poor winter pasture conditions followed unseasonable pasture growth. Average mating weight was greater with the lightest stocking rate in year 3 and with EW in years 1 and 2. Condition score generally followed weight patterns. In the 3 years, calf birth weight tended to be higher in EW, except for increased birth weight in EA in a year of unseasonable pasture growth. Average calving percentage and interval between successive calvings were 87% and 365 days, respectively, with no clear treatment trends. Overall average gross margins/ha ($A) for the lightest to heaviest stocking rates, respectively, were 126, 141 and 142 in ES, 93,109 and 118 in EA, and 54, 70 and 84 in EW. In general, ES enabled mainly heavier carcasses to be sold at seasonally favourable prices but resulted in some calf scours. Relative to ES and EA, EW calving tended to result in less cow stress in most years but heavier birth weights, more dystocia and lighter weaning weights if prolonged unseasonable pasture growth did not occur. Calf response to pasture conditions was generally proportional to calf age, and spring growth was probably affected by the level of milk consumption and calf growth potential relative to age. Post-weaning calf growth did not differ consistently with calving season. The relationship between animal performance and pasture condition may be useful for assessing different calving seasons in other environments.

The effect of mitochondrial DNA on milk production and health of dairy cattle

Maternal lineage effects, probably indicative of mitochondrial DNA (mtDNA) differences, may be important for milk production and reproductive success in dairy cattle ( Bos taurus). Sequence variation of mtDNA in 36 maternal lineages of dairy cattle was studied with animal models to assess effects on milk production and reproductive traits. Cattle within maternal lineages defined by registered pedigrees were assumed to be uniform for the nucleotide sequences examined. Sequence polymorphisms of bovine mtDNA were shown to be associated with milk production, reproduction, and health costs incurred. One particular base-pair substitution was associated with additional production of 842 kg milk and 37 kg milk fat per cow per lactation. Another single base-pair substitution was associated with a decrease of 36 days and one unsuccessful breeding between successive calvings. Effects of this size are economically important and have broad implications in genetic selection of dairy cattle.

Beef production from the dairy herd: calving performance of cows

Abstract Data are reported on the calving performance of cows in beef production trials in three successive calvings of South Auckland herds. The main comparison of Friesian, Hereford, and Charolais sires over the Jersey cow is supplemented by information on the Friesian cow mated to these three sire breeds and on straightbred Jersey and straightbred Angus calvings. Overall, 81% of calvings were unobserved. Eight percent of all calvings, or 45% of observed calvings, were assisted. Jersey and Friesian cows required more assistance when calves were sired by Charolais and Friesian sires, and least when Hereford sires were used. Cow mortalities at calving time were greatest for Jersey and Friesian cows in-calf to Charolais sires. Perinatal calf mortalities accounted for 3.5% of all calves born, with a greater mortality of calves by Charolais sires than other breeds. Calves assisted at birth were heavier than those from unassisted calvings, but gestation lengths did not differ significantly. Calves dying at bi...