Reproductive efficiency and body temperature in selected herds of Bos Taurus dairy cattle in East Africa

Abstract

Herds of Friesian and Jersey dairy cattle in three climatically contrasting regions of East Africa were involved; Njoro, in the Kenya Rift Valley; Kampala, to the north of Lake Victoria in Uganda; and Mombasa, on the Indian Ocean. All locations were close to the A equator. Differences in climate resulted from the variations in altitude. An analysis vas made of the herd records, but vas limited in ~cope as a result of the small number of records available, particularly at the Lake and Coast. Differences in milk yield between the Jersey herds were small. There vas a noticeable fall from the Rift through to the Coast in the Friesian yields. Corrections for the effect of high ambient temperature rendered the three herds similar. Calving interval ranged from a mean of 381 to 439 days, with no marked differences .between locations. The Rift herds shoved highly significant (P<O.Ol) positive correlations between current 305-day lactation yield and current calving interval (r = 0.80 and '0.92). Coefficients vere also positive at the other locations d by 12 days (r = 0.68, P(O.Ol). By plotting the monthly variations in calving frequency at each location, it appeared that a greater percentage of conceptions occurred during the rainy seasons, despite the practice of year-round calving policy. For the 40 cows under experiment in each herd, there tended to be a gradation in reproductive efficiency (time to first observable oestrus, oestrous cycle regularity, service period and non-return rate) from the temperate 'control' (Rift) through to the Lake. It was very noticeable that in certain cases, despite the very hot, humid conditions, the Coast herds suffered less reproductive disturbance than those at the Lake. There was little difference in overall fertility between the .two breeds. The effect of weather upon body temperature was measured using a Temperature Humidity Index~ T.B.I. = 0.4 (Td + Tw) + 15 where Td = dry bulb temperature in degrees Farenheit, and Tw = wet bulb temperature in degrees Farenheit. Time and afternoon rectal temperature were highly significant at the Coast (P(O.OOl). Temperatures rose o 0 by 0.22 F and 0.25 F per unit rise in T.H.I. for the two herds. Indices were invariably between 76 and 82. With the rise in altitude, T.H.I. decreased at the Lake and Rift and so also did the extent of body temperature elevation. Previous reports from climate control chambers indicated that 74 is the crucial Index, below which cattle remain in their neutral zone and above which body temperature tends towards the upper critical level. This was found to be the case for the Lake herds, temperature o rising 1.00 and 0.83 F for each unit increase in T.H.I. above 74. Large diurnal fluctuations in body temperature occurred at all locations, whatever the night-time T.H.I. Lack of insolation at the Coast obviously provided a great deal of relief, as also did shade during the day. Temperature variations during the oestrous cycle followed a typical low-high-low pattern over oestrus itself with a gradual rise as the luteal phase progressed. The curves were successively flatter from the Rift to the Coast. Contrary to suggestions in the literature, level of milk yield had no significant effect upon body temperature at the Lake or Coast. At the Rift however, high yielding cattle actually had significantly lover rectal temperatures. Rectal temperature measured at a depth of 18 cm was 0.570F higher than that at 10 cm (P<O.OOl). There were no differences in rectal temperature for the first 15 days following successful and unsuccessful services for the Rift herds. At the Lake and Coast, unsuccessful services had significantly higher temperatures over the 4 - 10 day period (levels of significance varied between 0.4 - 0.01 per cent). This is consistent with reports in the literature for cattle, sheep and the smaller laboratory mammals. It was not possible to determine the precise elevation of body temperature at which embryo failure might have occurred, but it was probably in the region of 103.0o 103.5 F. It would appear that adaptation played an important role in maintaining the reproductive efficiency of the Coast herds at a level comparable with that of the Rift. Correlations between T.H.I. at 1500 hrs East African