Researches into sterility of cows in South Africa. The influence of dry rations, lack of exercise, and lack of sunlight on reproduction of beef heifers and cows

Abstract

1. The effects of a dry ration, high condition, and the restriction of sunlight, and exercise upon sexual activity and reproduction of beef females have been studied. The observations were conducted on 30 grade (mostly half-bred) Sussex-Afrikander females. The experiment was commenced when the heifers were 15 months old and its duration extended over a continuous period of approximately 13 years. A small number of the animals was eliminated soon after the commencement of the experiment, but 60 per cent. remained under observations for 9 to 13 years. The period of the experiment includes 12 calvings. 2. When a dry ration consisting of maize, wheaten bran and teff hay was fed for nine months of each year and maize silage of good quality was added during the remaining three months of each year, very satisfactory results of growth and reproduction were obtained. Beef heifers from the age of 15 months attained a satisfactory mean weight of approximately 900 lb. at maturity or when about 24 months of age. Mature animals maintained good condition on the ration and they were able to acquire considerable weight during the pregnancy periods in most cases resulting in very high condition. Sexual maturity was reached before the age of 24 mouths and sexual activity and reproduction cannot be said to have been affected adversely by the treatment. 3. High condition caused no ill-effects upon general health or the reproduction processes. 30 per cent. of the cows lived to the age of 14.4 years. The total pregnancies were 206, 191 calves were born, 15 abortions occurred. The mean calf production of all groups was 6.4 per cow. 4. The restriction of sunlight and exercise in no way detrimentally affected the health, growth and vigour of heifers and cows; being fed dry rations. There was no significant difference in the body weights of the comparative Groups A and C which attained 957.8 and 995.9 lb. at the age of 31 months respectively. The onset of maturity was not delayed. Up to the age of 31 months, or prior to being bred, a large number of dioestrous cycles were seen to have been experienced by the heifers receiving restricted sunlight and exercise. The mean number of dioestrous cycles experienced by the restricted groups was 15.5 as opposed to 12.2 in the unrestricted group. Considering all groups, the mode of the period of dioestrus was 20 days, and, although cycles as short as 10 days and as long as 123 days were experienced, approximately 75 per cent. of the dioestrous cycles fell between 18 and 23 days. It appears that as the age of the animals advanced under the treatment enforced the percentage of dioestrous cycles between 18 to 23 days decreased. Considering all groups for all periods, during which time 881 dioestrous cycles were observed, the mode was 20 days, 21.1 per cent. being of that duration. In 69.5 per cent. of cases the periodicity of oestrus was 18 to 24 days. 5. A restriction of sunlight and exercise did not affect the period between calvings. In all groups for the entire experimental period in 44.5 per cent. of cases, the period between calvings was 12 months. In the restricted exercise group in 51.1 per cent. of eases the period exceeded 12 months whereas in the group receiving exercise the equivalent figure is 50 per cent. Generally oestrus was observed to occur 15 to 21 days after calving. Although, in the majority of cases the period of absence of oestrus was in the vicinity of 60 days, many cases of over 100 days occurred and cases of even over 200 days were encountered. 6. Restricted sunlight and exercise had no effect upon conception rate. In the restricted group, 72.1 per cent. of cows were impregnated by one service, and the equivalent figure for the unrestricted group was 81.1 per cent. The percentages impregnated by 1 and 2 services is 80.9 per cent. and 90.5 per cent. respectively. Considering all groups only 5.8 per cent. required more than four services to establish pregnancy. 7. The lengths of gestation was unaffected by limiting sunlight and exercise. The mean gestation period up to the age of 6 years was 280.5 days; gestation periods during later periods or in older cows was 277.4 days, the difference being significant. 8. Unrestricted exercise and sunlight did not reflect any advantage upon the weight of calves produced. A suspicion exists that the use of different bulls during the course of the experiment influenced the birth weight of the calves during different periods. Considering all groups, few calves born weighed under the 60 lb. at birth, while weights up to 99 lb. were recorded. There is a tendency for lighter calves to be horn with advancing age of cows. 9. High-conditioned heifers, under conditions of restricted sunlight and exercise, showed no tendency towards abnormal sexual activity when breeding was delayed until the heifers were 35 months of age, that is, they calved down at 44 months of age. The reproductive functions and regularity of calving were unaffected by such delayed breeding. The disadvantage was that, over the lifetime of the cows, only 59 calves were obtained as compared to 66 in each of the groups bred six months earlier. 10. The environment enforced appears to improve the expectation of life and reproduction of beef cattle on the high veld of the Transvaal. This is, no doubt, due to protection from cold and ticks, as well as from diseases, such as contagious abortion and trichomoniasis, affecting the genital tract. 11. There is a predisposition to the development of cystic degeneration of the Graafian follicle during advancing age in cattle maintained under the environmental conditions enforced even when they are protected from genital infection by suitable hygiene.