No abstract

A survey of 50 Friesian/Holstein dairy herds (average size 178 cows) in England investigated the rate of culling and the reasons for disposal and death over three years from 1990 to 1992. The average total annual culling rate was 23.8 per cent (22.0 per cent sold and 1.8 per cent died). Of the disposals, 54 per cent were culled by the end of their fourth lactation. Poor fertility was the most important reason for culling (36.5 per cent of disposals), followed by management policy (11.5 per cent), mastitis (10.1 per cent), bovine spongiform encephalopathy (BSE) (7.4 per cent) and lameness (5.6 per cent). The most common causes of death were mastitis (8.9 per cent) and BSE (11.5 per cent), but 46 per cent died for unknown reasons.

The Dairy Information System (DAISY) was developed to record fertility and health information for use in research and to help farmers manage their farms. Data from 33 herds recording health and fertility over a 6-year period were used to study genetic relationships of several health, fertility and production traits. There were 10 569 records from 4642 cows of all parities. These were used to estimate genetic parameters for health: mastitis, lameness and somatic cell score (SCS), for fertility: calving interval, days to first service, conception to first service and for production: 305-day milk, butterfat and protein yields. Heritabilities for these traits were also estimated for the first three lactations. (Co)variances were estimated using linear, multitrait restricted maximum likelihood (REML) with an animal model. Mastitis and lameness were treated as all-or-none traits. The incidence of these diseases increased with lactation number, which may lead to variance component estimation problems, as the mean is linked to the variance in binomial distributions. Therefore, a method was used to fix the within-lactation variance to one in all lactations while maintaining the same mean. The heritability for SCS across lactations was 0·15. Heritabilities for other health and fertility traits were low and ranged between 0·013 and 0·047. All genetic correlations with the production traits were antagonistic implying that selection for yield may have led to a deterioration in health and fertility. The genetic correlation between SCS and mastitis was 0·65 indicating that indirect selection for improvements in mastitis may be achieved using somatic cell counts as a selection criterion. The potential use of linear type scores as predictors of the health traits was investigated by regressing health traits on sire predicted transmitting abilities for type. The results indicate that some type traits may be useful as future selection criteria.

The incidence of major production diseases and other health problems was investigated in 90 Friesian/Holstein dairy herds in England (average size 152 cows) for cows calving during 12 months in 1992-1993. The mean incidence of mastitis was 33.2 cases per 100 cows, and it affected 20.6 per cent of the herd with 1.6 cases for each affected cow. On average, 17.4 per cent of the cows suffered from lameness, with 1.4 cases per affected cow and a total of 24.0 cases per 100 cows. Cows treated for oestrus-not-observed totalled 33.6 per cent, with 46.4 treatments per 100 cows. The incidence of milk fever was 7.7 cases per 100 cows. Retained fetal membranes affected 3.6 per cent of cows. Vulval discharge affected 15 per cent of the average herd with 1.4 treatments per affected cow and a total of 21.2 treatments per 100 cows. The mean incidence of twinning was 4.1 per cent. Calf mortality claimed 7.8 calves per 100 calves born. The average number of cows given aid at calving was 8.7 per 100 cows calving.

The associations between periparturient diseases in 3603 lactations over three calving seasons were assessed on 10 dairy farms in the south west of England by using logistic regression. Calf mortality and dystocia were strongly associated. Twinning and dystocia were important predictors of calf mortality. Twinning was also a significant predictor for retained fetal membranes. Retained fetal membranes, twins, calf mortality and dystocia, in that order of importance, were risk factors for vulval discharge. Twinning, dystocia, retained fetal membranes and lameness before service increased the risk of mastitis before service. Similarly, mastitis and dystocia before service increased the risk of lameness before service. Oestrus was less likely to be observed in cows that had twinned or suffered lameness before service, the latter having a significantly greater influence in first calvers than older cows.