Ten dairy herds reporting acute fertility problems were investigated by analysing records and cows, metabolic profiles, tests for infectious agents and milk hormone assays. The main problems were : heat detection (2), endometritis (3) and inadequate nutrition (5). In one herd no cause has yet been identified. On all farms the problem had been present from the start of the breeding period. Management changes, delayed analysis of herd records and over-estimation of forage nutritive value were underlying problems. A diagnostic analysis/decision process to highlight problems early is essential to minimise loss.

The survival and fertility of strains of Holstein-Friesian (HF) cows, Jersey cows and their crosses was investigated. Parametric survival analysis was used to model the number of days between first calving and last known herd test. The analysis was stratified by breed and included explanatory variables for production and nonproduction traits and proportion of overseas (i.e. not of New Zealand origin) HF genetics. Linear model analyses were used to investigate the genetics of fertility measures of first—lactation cows and their associations with production, live weight and survival. The HFJersey crossbred cows had a lower risk of culling than the parental breeds. The risk of culling increased with the proportion of overseas HF genes in both the HF and HFJersey crossbred cows. The heritabilities for the fertility traits ranged from 1.3% to 5.4% with days from start of mating to first mating (DFM) having the highest value. Antagonistic relationships, in terms of genetic correlations, between fertility and production were largest for DFM. DFM was negatively correlated with survival. Declining fertility and survival were found as the proportion of overseas HF increased.

The resumption of reproductive activity in the early post partum period and the subsequent fertility of dairy cows are of considerable practical and economic importance to the producer. Regular milk progesterone analysis was used in this study to monitor the re-establishment of reproductive cyclicity in animals of average (AGM, n=20) and high genetic merit (HGM, n=28) kept under standard management conditions. The profiles obtained were then characterised into normal and four different types of abnormal activity. Resumption of cycles occurred significantly later in the higher yielding cows than in those of average genetic merit (23 ±2.3 days in HGM cows and 15 ± 1.6 days in AGM cows; P=0.0089). There was a significant increase in the amount of abnormal cycles encountered in the high genetic merit animals compared with average yielding animals (61% and 30% respectively; χ2 test, P=0.045); in particular, the delayed occurrence of ovulation post partum (11% vs 0%) and an increased incidence of persistent corpora lutea (32% vs 20%). For high genetic merit animals, the incidence of abnormal cycles was associated with increased peak milkyields (abnormal cycles: peak milk yield 54.7 ± 1.11 kg/day; normal cycles: peak milk yield 46.4 ± 1.35 kg/day, P=0.002). This relationship was not apparent in average genetic merit animals. First service conception rates were 50% (9/18) for AGM cows and 38% (10/26) for HGM cows (χ2 test, n.s.). The calving to conception interval was 98 ± 9.7 days for AGM animals (n=l7) and 105 ± 9.1 days for HGMs (n=24) (t-test, n.s.). In conclusion, this study confirms that high genetic merit dairy cows have compromised reproductive function in terms of a delayed resumption of cyclicity and an increased incidence of abnormal progesterone cycles, which was associated with higher peak milk yields. There was also a reduced first service conception rate in high yielders although the difference was not significant with this group size.

Based on their pedigree indices for milk production traits, 48 high (HM) and 48 medium (MM) genetic merit cows were studied in each of two years to determine the possible relationships between genetic merit, milk production, body condition, metabolite and hormone concentrations, feed intake and reproductive performance. The high genetic merit cows had higher milk production, greater body condition loss between calving and first service, lower plasma glucose and insulin-like growth factor-1 (IGF-1) and lower first and second service conception rates than the medium genetic merit cows. Furthermore, more high genetic merit cows were not pregnant at the end of the breeding period compared with medium genetic merit cows. Cows that did not conceive to first service were retrospectively compared to those that conceived to first service within each genetic merit category. Within the high and medium genetic merit category there were no significant differences between the cows that did not conceive and those that conceived to first service in terms of milk production, or plasma concentrations of glucose, non-esterified fatty acids (NEFA). Although medium genetic merit cows that did not conceive to first service lost more body condition score between calving and first service than those that conceived to first service, there was no difference in body condition score (BCS) change between calving and first service between high genetic merit cows that did not conceive and those that conceived to first service. In the present study, high genetic merit cows had higher milk production and reduced reproductive performance in comparison with medium genetic merit cows. However, reproductive performance was not associated with milk production, energy balance or plasma concentrations of glucose, NEFA or IGF-1 between calving and insemination

In Belgium, both dairy and beef cattle are managed intensively. Three commercial farms owning both a Belgian Blue —double muscled type- suckler beef herd and a Holstein-Friesian dairy herd were surveyed between 1994 and 1998. The aim of the study was to compare growth and reproduction performances of both breeds in a similar farm environment. The replacement heifers of both breeds were kept together until advanced pregnancy. Reproduction data were collected monthly from heifers older than fourteen months. The live weight of the replacement heifers was recorded quarterly until 20 months of age. Breed influenced the growth of replacement heifers at 6, 9 and 12 months (P < 0.001). The growth rate of Belgian Blue heifers was reduced after the age of one year and the live weight difference between breeds was not significant anymore. Belgian Blue heifers were always heavier than Holstein-Friesian heifers. Successfully bred heifers had a greater growth rate than non successfully bred heifers within the Belgian Blue breed. This was significant for the weight at 6 months (P < 0.05) and at 12 months (P < 0.05). Such an effect was not detected for the Holstein-Friesian breed (P > 0.05). Weight was not a limiting factor for fecundity of the Holstein-Friesian heifers. Management policies other than growth performance explained the difference between optimal fecundity and the fecundity index met in this study. Non successfully bred Belgian Blue heifers were lighter than successfully bred animals. Unsufficient weight performance had an impact on fecundity in that breed.

Dairy cows in confinement and pasture-based feeding systems were compared across 4 spring-calving and 3 fall-calving replicates for differences in reproduction, mastitis, and body condition scores. Each feeding system and replicate included both Jersey and Holstein cows. Cows in confinement were fed a total mixed ration with maize silage as the base forage along with a variety of concentrates. Cows on pasture were routinely supplemented with concentrates and were provided baled grass and/or legume silage when pastures were limiting. Breeding periods were for 75 days in spring or fall. Reproductive performance did not differ significantly due to feeding system but Jerseys had higher conception rates (59.6 vs. 49.5%) and overall pregnancy rates (78.0 vs. 57.9%) than Holsteins. Cows in confinement had significantly higher rates of clinical mastitis and culling for mastitis than cows on pasture. Within both feeding systems, Jerseys had less mastitis than Holsteins. Average body condition scores were higher for confinement cows than pasture cows except for one replicate. Jerseys maintained higher average body condition scores than Holsteins in all but one replicate. In summary, pastured cows produced less milk and had less mastitis but lower body condition scores than confinement cows. Holsteins produced more milk but were less likely to rebreed, had more mastitis, higher culling rates, and maintained lower body condition scores than Jerseys.