Effects of body weight and condition changes after parturition on the reproductive performance of Sahiwal and Friesian cattle
Nutrition has a profound influence on reproductive performance after parturition. Cows are in a typical state of negative energy balance, because nutritional requirements for milk production and maintenance of body function exceed that ingested from the feed. This is reflected by changes in body weight and condition postpartum which influence resumption of ovarian activity. The study objectives were to assess weight and body condition changes after parturition and their influence on reproductive performance of Sahiwal and Friesian lactating cows. Forty in-calf cows comprising 20 Friesians and Sahiwals were selected and upon calving, observed for 24 weeks postpartum. Parameters recorded were weekly live weight and body condition scores postpartum while reproductive attributes included days to commencement of luteal activity and insemination. Data were analyzed using GLM of SAS. There were breed differences in weight of cows at the start of the experiment with Friesians being heavier than Sahiwals. Friesians lost a mean of 31.2 Kg from calving to commencement of luteal activity which occurred 10 weeks postpartum and improved from this loss to register a deficit of 11.3 kg at insemination which occurred 14 weeks after calving while the Sahiwals lost a mean of 27 kg after 6 weeks postpartum at commencement of luteal activity and a further 8 kg to insemination occurring 10 weeks after calving. The mean weight loss for Friesians from calving to commencement of luteal activity was 0.45 kg/day while that of Sahiwals was 0.64 kg/day. The relative weight loss was 6 and 7% for Friesians and Sahiwals respectively. The mean body condition loss for the two breeds showed Sahiwals lost less body condition at commencement of luteal activity than Friesians (-0.19 vs -0.33) and resumed cyclicity earlier than Friesians which had better recovery rates from weight and body condition depression postpartum. This shows that Friesians lose weight rapidly and quickly recover at time of insemination while the weight loss for the Sahiwals is gradual and takes longer to recover. Friesians showed weight recovery after 15 weeks postpartum and this is when insemination occurred, while the nadir of weight depression occurred between weeks 5 and 7 postpartum and coincided with peak milk production. In both breeds insemination occurred 4 weeks after commencement of luteal activities. The Sahiwal depression was gradual and the recovery trends were not so clear-cut. The mean body weight at calving for Friesians inseminated and calved was 427kg compared with those that did not calve averaging 451kg while Sahiwals that calved had a mean weight of 381kg compared to those that didn’t averaging 389kg. This is an indication that heavier cows had difficulty in conceiving. There was a positive association between body weight and condition scores postpartum in Sahiwals while Friesians exhibited a negative association, due to the differences in adaptation to negative energy balance after parturition for the two breeds.