R. F. Veerkamp

Genetic aspects of common health disorders and measures of fertility in Holstein Friesian dairy cattle

The purpose of this study was to estimate genetic parameters for measures of fertility and several health disorders in dairy cows. Data consisted of 33732 records, of which 9163 were on heifers, on 305-day milk yield, health disorders and inseminations. Measures of fertility were calculated from calving and insemination dates and included calving interval, days to first service and conception to first service. Health disorders included milk fever, mastitis and lameness. Genetic and phenotypic (co)variances were estimated using restricted maximum likelihood. Heritability estimates for both health disorders and fertility traits were low, ranging from 0·003 to 0·080. All genetic correlations between 305-day milk yield and health and fertility traits, in cows and heifers together, were antagonistic implying that selection for milk yield may have caused a deterioration in health and fertility. The unfavourable correlation between milk yield and health and fertility traits, plus the economic importance of the latter, suggests that future breeding goals should be expanded to include some health disorders and fertility.

Genotype and feeding system effects and interactions for health and fertility traits in dairy cattle

The effects of feeding system, genotype and genotype by feeding system interactions on a range of health and fertility traits were investigated in Holstein Friesian cows at the Langhill Dairy Cattle Research Centre. There were two genetic groups: a selection (S) and control (C) line, housed and managed as one herd. Animals from each group were assigned to either a high concentrate (HC) or low concentrate (LC) feeding system and offered approximately 2500 kg and 1000 kg of concentrate per lactation on the HC and LC diets respectively. Feeding system had a significant effect on milk fever, days to first service and days to first heat. Lactation number had a significant effect (P<0.05) on the incidence of mastitis, ketosis, retained placentas, milk fever and lameness and conception at first service. Effects of genotype were investigated first by comparing the two genetic groups and then by regressions of the health and fertility traits on pedigree index for fat plus protein (PI). Significant effects of PI were found for oestrus not observed, conception at first service, days to first heat, calving interval, days open and days to first service. The regression coefficient for mastitis on PI was also significantly different from zero (P<0.05). There were no statistically significant genetic line by feeding system interactions, indicating that the observed line differences applied to both dietary treatments. Heritabilities for the health traits ranged between 0.00 and 0.08 and for the fertility traits they ranged between 0.02 and 0.15. Selection for high genetic merit in this herd, seems to have led to a deterioration in fertility but not health traits (with the exception of mastitis). These results, in line with those from studies in large populations, suggest that as genetic merit for production rises, fertility and some aspects of health are deteriorating.

Estimation of genetic parameters using health, fertility and production data from a management recording system for dairy cattle

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.

Genetic correlations between linear type traits, food intake, live weight and condition score in Holstein Friesian dairy cattle

Variance components were estimated from an animal model using a restricted maximum likelihood procedure which allowed for unequal design matrices and missing observations (VCE). Data sets containing: (i) 15 275 records of linear type classifications on heifers, (ii) 3399 live weight and condition scores measured at calving and (iii) 1157 records of yield, dry-matter intake, average live weight and condition score during the first 26 weeks of lactation; were analysed jointly. Heritability estimates for dry-matter intake, live weight and condition score in the largest data set were 0·44, 0·44 and 0·35 respectively and the genetic correlation between condition score and the yield traits ranged from −0·29 to −0·46. The genetic correlation between milk yield and average live weight was negative (−0·09) but after adjusting for the genetic variation in condition score this correlation was positive (0·29). Genetic correlations between live weight and stature, chest width, body depth and rump width were consistently high (0·52 to 0·64; 0·75 to 0·86; 0·59 to 0·81; 0·56 to 0·74, respectively). Chest width and body depth were little to moderately correlated with dry-matter intake (0·25 to 0·28 and 0·20 to 0·34 respectively), and angularity (−0·47 to −0·77) and chest width (0·32 to 0·73) appeared to be good predictors of condition score. These correlations showed that (i) the relative value of live weight compared with food intake capacity determines the optimum direction of selection for stature, chest width, body depth and angularity, and consequently the optimum size of the dairy cow, and that (ii) live weight, condition score and food intake can be predicted from the type traits with little loss in accuracy. A restricted index which maintains condition score at its current level was predicted to reduce overall (economic) genetic gain by 5%.

Effects of interaction between genotype and feeding system on milk production, feed intake, efficiency and body tissue mobilization in dairy cows

The objective of this study was to investigate genotype by feeding system interactions in Holstein-Friesian dairy cows. For this purpose, selection (S) and control line (C) cows, housed and managed at the Langhill Dairy Cattle Research Centre, were offered ad lib. complete mixed diets, with proportions (in total DM) of concentrates, silage and brewers grains of either 20:5:75 (LC) or 45:5:50 (HC), over a full lactation. No significant feeding system × genetic line interactions were observed for a number of traits, describing milk production, feed intake, efficiency and body tissue mobilisation, when compared as treatment means (128 heifer lactations and 249 cow lactations). However, regression coefficients of milk yield (P < 0.01) and condition score (P < 0.05) on pedigree index for fat plus protein yield were significantly different between LC and HC. This indicates that G × E might become of importance in the future, with continued selection for fat plus protein yield.

Selection for longevity and yield in dairy cows using transmitting abilities for type and yield

A dynamic programming model was used to derive economic values for the goal traits milk, fat and protein yield and longevity. The economic values derived were £3.37 per % cows surviving to complete lactation four (conditional on having a milk record in the first lactation) and £-0.03, £0.60 and £4.04 per kg for milk, fat and protein yield respectively. In terms of genetic standard deviations the weight for protein, fat, milk and longevity were 1.0, 0.21, —0.25 and 0.55, respectively. Using economic values and genetic (co) variances, weights were derived for milk fat, protein and four linear type traits (chosen out of fifteen on the basis of the genetic correlation with longevity): angularity (angular), foot angle (steeper), udder depth (shallower) and teat length (shorter). Three additive indices were derived, assuming that the breeding goal was for: (i) yield only (PIN), (ii) longevity only (LIN) or (ii) yield and longevity, hence economic merit (ITEM). Selection on ITEM is expected to give a 2% higher annual rate of genetic progress compared with selection on PIN. Efficiency of using ITEM was larger than 0.97 compared with the optimum index, when the real individual economic values increased or decreased by a factor 1.5 or 2.0. Weights for ITEM were calculated assuming that predicted transmitting abilities (PTAs) from complete multivariate analysis were used as index measurements. In the practical situation that index measurements came from (i) separate univariate best linear unbiased prediction (BLUP) evaluations or (ii) two multivariate BLUP evaluations (one for type and one for yield), efficiency of ITEM (compared with the optimum index) decreased with decreasing accuracy of the PTAs and with increasing ratio between number of records for type and yield, or vice versa, but remained close to 100%. Only in the (not practical) situation where accurate PTAs for type and inaccurate information for yield were combined, did the efficiency of ITEM drop as low as 0.44, due to a change of sign for udder depth in the optimal index.

Predicting breeding values for herd life of Holstein-Friesian dairy cattle from lifespan and type

Data comprised information on herd life from two different sources: actual lifespan and type data. The optimum way of predicting breeding values (BVs) for herd life from both these sources is a multivariate best linear unbiased predictor (BLUP) analysis of lifespan and the linear type traits most closely related to it. To reduce computing requirements, we suggest a bivariate BLUP analysis, where the direct information is lifespan, measured in lactations and the indirect information is a phenotypic index of type traits weighted by their economic values. Such an index is shown to be almost as efficient as using the individual traits. Genetic correlations between functional lifespan and the linear type traits were estimated, and based on these foot angle (rg = 0·22) udder depth (rg = 0·24) and teat length (rg = -0·44) were chosen to predict herd life. Breeding values for herd life were predicted in a BLUP analysis for around 500 000 heifers. The traits were lifespan and the phenotype index offoot angle, udder depth and teat length. For bulls with a minimum of 10 daughters BVs ranged from -0·9 lactations to +1·0 lactations, indicating a difference of approximately one lactation between the daughters of extreme bulls. For sires with at least 50 daughter records for lifespan, type information contributed little to the accuracy of herd life BVs.

Risk factors associated with the incidence of ketosis in dairy cows

Various dairy cattle production and health characteristics were studied with a view to identify easily available and measurable factors associated with the incidence of ketosis. The analyses were carried out using data from the Langhill Dairy Cattle Research Centre. Two approaches were used to assess the relative risk to cows of getting ketosis: one using information known at the beginning of lactation and one 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 live weight 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.

Effects of genotype, feed type and lactational stage on the time budget of dairy cows

The effects of genetic merit, feeding system and stage of lactation on the time budget of dairy cows were studied. Sixteen loose-housed Holstein Friesian cows (parity=1) of either high or UK average genetic merit were fed one of two complete mixed silage-based diets (high and low concentrate inclusion). Five-minute time samples were carried out on 11 days across lactation between morning feeding and afternoon milking. Cows fed the low concentrate diet spent more time eating, more time ruminating whilst standing, and less time lying, especially inactive. Genetic line did not affect the time budget of the cows. Standing and rumination decreased with time from calving, whereas the duration of lying bouts increased during the first 3 months of lactation. In this study the time budget of dairy cows was influenced by food roughage inclusion, and not by the production level of the animal.

Effects of genotype and feeding system on the reproductive performance of dairy cattle

Potential factors influencing reproductive performance were examined in a high producing Holstein Friesian dairy herd. There were two genetic groups: a selection line (S) consisting of heifers and cows with the highest genetic merit for kg fat plus protein in the UK, and a control line (C) consisting of heifers and cows of average genetic merit for kg fat plus protein. Within each group, heifers were randomly assigned to either a high concentrate (HC: Annual average intake of about 2.5 ton per cow) or low concentrate (LC: Annual average intake of about 1.0 ton per cow) complete diet based on grass silage, brewers grains and concentrates. The mean milk yields during the first 26 weeks of lactation for cows in the S-HC, C-HC, S-LC and C-LC groups were 6008, 5254, 5041 and 4573, respectively. Data on the performance of 114 heifer lactations and 287 cow lactations was available for analysis. There were no significant differences in the mean intercalving interval, number of days to first observed estrus and number of services per pregnancy for selection versus control line cattle. Also, no difference in reproductive performance was observed between cows on the high concentrate and low concentrate diets, but heifers fed the high concentrate diet had significantly longer intercalving intervals than heifers on the low concentrate diet. Average condition score of cows during the first 26 weeks of lactation was negatively related to number of services per pregnancy and intercalving interval. The degree of body condition score loss in heifers and cows between calving and week 10 of lactation was negatively related to the number of days to first observed estrus. In heifers there was a significant positive relationship between milk yield during the first 26 weeks of lactation and number of days to first observed post partum estrus, and in cows milk yield was positively related to number of services per pregnancy and calving interval.