EFFECTS OF DIETARY PROTEIN LEVEL UPON PERIPHERAL PLASMA PROGESTERONE CONCENTRATION AND CONCEPTION RATE IN DAIRY CATTLE

Abstract

There have been concerns that high protein intake had a significant influence on blood components and uterine constituents in non-lactating dairy cows and on spcrmatozoal motility. There are study that show that as dietary crude protein (CP) is increased, there is a tendency of reduced fertility in dairy cows while other studies have suggested that there is no relationship between reproductive performance and dietary CP intake. The objective of the study was to investigate the effect of dietary CP intake on blood progesterone concentrations and conception rate in dairy cattle. Fourteen lactating Friesian cows were randomly divided into two equal groups, a control group - Low Protein (LP) and a treated - High Protein (HP) group. The cows’ oestrous cycles were synchronized and inseminated with frozen semen. Jugular blood samples were collected daily for at least 21 days after the first insemination starting on day of oestrus and then twice per week until they were 6-weeks of pregnant and then once per week until they were 12-weeks pregnant. The result showed that the progesterone concentrations in the control (LP) cows were significantly higher than in the treated (HP) cows during pre-conception oestrous cycles that did not result in pregnancy for 10 cows (5 in each group). Except on the last day of sampling (day 42), there were no differences in progesterone concentrations between the two groups of cows during first 6-weeks of pregnancy. The plasma progesterone concentrations were significantly lower in the HP group on days 45 and 52. However, dietary protein had no significant effect on overall group mean concentrations over this 6-week period (7 to 12 week) but the interaction, Group x time, was significant. The number of services per conception was lower for the cows fed the low CP diet. However, the median number of services per conception for the two groups was not statistically different. The results clearly indicated that cows fed the high CP rations had significantly reduced plasma progesterone concentrations when compared with those fed the low protein diet. The result also suggested that low progesterone concentrations particularly during the pre-conception oestrous cycle in the HP-fed groups were associated with a lower conception rate (32%) compared in the LP-fed group (54%).