Effects of selection for production and maternal diet on maiden dairy heifer fertility

Abstract

AbstractThe objectives of this study were to investigate reproductive performance and the influence of maternal environment on reproductive performance in two genetic lines of maiden heifers. These were given food and managed in the same way at the Langhill Dairy Cattle Research Centre. The two genetic lines were established in 1973; one has been selected for high combined yield of fat plus protein (selection line; S) and the other has been maintained at around the UK average for genetic merit of yield of fat plus protein (control line; C). Analysis of the reproductive performance of 988 heifers born between 1981 and 1998 showed that S heifers were poorer (all P < 0·05) than C heifers for all reproductive measures: conception at first service (S: 0·64, s.e. 0·02; C: 0·71, s.e. 0·03), interval between first and last service (S: 18·2 days, s.e. 2·2; C: 13·4 days, s.e. 2·2) and number of services per conception (S: 1·49 services, s.e. 0·06; C: 1·39 services, s.e. 0·06). S heifers were also younger at first service than C heifers (474·9 days v. 480·1 days, s.e. 1·9, for S and C respectively; P • 01). Fertility of service sires may have had some influence on these results, but this could not be investigated here, as S heifers were mated only to high merit bulls and C heifers to average merit bulls. However, within genetic line, the yearly downward trend in the average number of services per conception of heifers was significantly different from zero for the S line, but not the C line. There were no statistically significant relationships between conception rates in maiden heifers and their subsequent reproductive performance in first lactation. The effect of maternal environment on the reproductive performance of daughters as maiden heifers was investigated. There were no statistically significant relationships between daughter reproductive performance and dam parity or the feeding system of the dam (either a high or low level of concentrates). Within the limited range of nutritional status of dams during the periods post calving and in early pregnancy, there was no statistically significant effect of maternal nutrition on daughter reproductive performance.