Effects of nutritional supplementation and genotype on milk production and fertility of lactating dairy cattle under tropical conditions
The objective of this study was to determine effects of nutrition on milk production and fertility in lactating multiparous Friesian and Sahiwal cows. Forty in-calf cows comprising 20 Friesians and Sahiwals were selected and upon calving were randomly assigned to 5 dietary groups consisting of concentrate supplementation at the rate of 0, 1, 2, 3 and 4 kgs fed twice per day after grazing on pasture for 24 weeks postpartum. Each feeding level comprised 4 Friesians and 4 Sahiwals. Pastures and concentrates were analyzed using proximate analysis. Milk samples were collected weekly to determine composition using infrared spectroscopy while blood was collected bi-weekly to determine progesterone levels using radioimmunoassay. Parameters recorded included milk yield and composition (%fat, %protein, %solids not fat (SNF) and density. Reproductive data included days to beginning of luteal activity (progesterone >3nm/L) and days to 1st insemination. Data were analyzed by GLM of SAS. Feeding levels, breed by feeding levels, parity, weight of cow significantly affected milk yield. Heavier cows produced more milk with a mean increase of 0.2kg for each increase in weight. Feeding level 4 had the highest mean milk yield per week (p<0.05) in both breeds averaging 72.2±4.4 and 43.1±1.7 liters for Friesians and Sahiwals respectively. Breeds differed for days to peak milk production and peak milk yield with Friesians and Sahiwal cows averaging 31.6±6.0 and 42.2±3.8 days to reach peak milk yield, while peak milk yields were 79.5±5.9 and 58.4±2.7 liters respectively. Significant breed differences were also observed for %fat, protein, SNF and density of milk. Sahiwal exhibited better reproductive performance than Friesians. It was observed that 18% of in-calf cows lost their foetus before term and 25% of them never showed heat 120 postpartum. Of these, 15% never showed any luteal activity, while 10% had silent heat. Sahiwals came into heat and started cycling earlier (p<0.05) than Friesians. Friesians had more (p<0.05) cows conceiving at 1st insemination and showing luteal activity later than the Sahiwals. There was within breed and between Feeding levels differences (p<0.05) for days to 1st heat and start of luteal activity. However the outcomes were varied and did not show specific patterns for Feeding level effects in both breeds. It can be concluded that breed effects were more important than the nutritional effects on milk production, composition and reproductive performance.
Key Words: Dairy; Nutrition, Fertility; Milk production