HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Chapman, A. B. Articles by Casida, L. E. Search for Related Content PubMed Articles by Chapman, A. B. Articles by Casida, L. E.

Factors Associated with Breeding Efficiency in Dairy Cattle¹

University of Wisconsin

Abstract

An efficient dairy brood cow is one which produces her first normal living calf at a certain optimum age and another every 12 to 13 months for a number of years thereafter. In order to meet this standard of reproductive efficiency a cow must conceive as a heifer at an age early enough to utilize efficiently her full reproductive and productive powers throughout life, and succeeding conceptions must be within 85 to 115 days following calving if the next parturition is to occur within the 365- to 400-day interval following a normal gestation period.

If a cow is to conceive and produce normal living calves regularly, it is imperative that those factors which are associated with the recurring production, fertilization and implantation of normal ova, and with the development of the embryo and foetus until it is expelled as a viable healthy calf, should also occur regularly. The final explanation of these phenomena will undoubtedly come from physiological studies, but until such results are available, certain leads may be found and problems suggested by statistical analyses of breeding records. It was with this in mind that the records of a Wisconsin herd were studied. In this particular herd careful breeding records are kept, conditions of the animals are closely followed and rectal examination of the ovaries is made in doubtful cases.

One of the outward expressions of the reproductive cycle is heat or oestrus. If the dairy cow does not manifest symptoms of oestrus, the probability of regular conception is very much reduced, irrespective of whether the cycle is otherwise normal.

The cows reported here were divided into two groups. One group, termed clinically normal, showed no cystic follicles or retained corpora lutea during the entire period covered by these records. The other group, clinically abnormal sometime during life, includes those which had cystic follicles or retained corpora lutea in at least one calving interval.

The average length of the period from parturition to the first oestrus following, on 179 such periods preceded by normal gestations in clinically normal cows, was found to be 69 days, with a standard deviation of 39 days. This variation in the length of parturition-to-first-oestrus-following was divided into that between cows and that between calving intervals of the same cow averaged over all cows. The skewness of the distribution and the unequal frequencies in each class have made it difficult to evaluate the amount of variation which can be attributed to real differences between cows, but it would seem that within a fairly wide range of variation a cow tends to repeat a similar length of parturition-to-first-oestrus in different calving intervals. The breeding efficiency of a cow is, therefore, inherently lowered when this period in her reproductive cycle is so long that she cannot conceive in the 85- to 115-day interval.

In the calving intervals preceding the ones in which cystic follicles or retained corpora lutea were noted in the clinically abnormal cows, the period from parturition to first oestrus was 71 days, which was not significantly different from the length of this period in the calving intervals following the ovarian disturbance, and neither of these figures differed significantly from that for the clinically normal animals.

The study of the oestrus cycles in the clinically normal cows was limited to calving intervals following non-abortive parturitions. For the purposes of this study all intervals between successive recorded heats are treated as "oestrus cycles." These intervals varied from 2 days up to nearly 200 days. The oestrus cycles, so defined, were divided into two groups—those which immediately followed an infertile service (copulatory oestrus cycles), and those which were not preceded by copulation (non-copulatory oestrus cycles). The modal length of both of these groups of cycles was 21 days, but the means of the two groups differed markedly from this and from each other. The non-copulatory cycles averaged 32 days, and the copulatory 37 days. This difference between the two classes of cycles is brought out more clearly by the proportional distributions of the cycles in the two groups. Of all non-copulatory cycles, 63 per cent fell between 17 and 27 days, while only 56 per cent of the copulatory cycles were found in this central group. In the group 28 days or more in length there were 41 per cent of the copulatory cycles as compared to 31 per cent non-copulatory cycles.

Quiet heats or failure to observe heats would probably explain many of the longer cycles. Therefore, in order to study these variations more exactly, all cycles over 33 days were excluded, thereby avoiding most of the periods which contained two or more oestrus cycles. The remaining data then fall into approximately normal frequency distributions. After this treatment the mean of the non-copulatory group became 21 days, and of the copulatory group 22 days, the difference being significant. The greater average length of the copulatory cycles might be ascribed to a physiological reaction of the ovary to copulation, or to a temporary reproductive disturbance at the time of or subsequent to service. Such disturbance might result in failure either in fertilization or implantation, or in early resorption of the embryo.

Hammond¹ reports the length of the oestrus cycles in three heifers following mating to a vasectomised bull. He states that, if there is any effect of service, it is to decrease the length of the subsequent cycle. If Hammond's findings are confirmed by larger numbers the difference between his results and ours may lie in the fact that the bulls in our study all showed good general fertility, whereas Hammond used a definitely sterile bull.

The copulatory and non-copulatory cycles of the clinically abnormal cows were divided into two groups, those found in the calving intervals which preceded the one in which the ovarian abnormality was noted and those which succeeded it. The variation in length of the non-copulatory cycles of the clinically normal cows was very similar to that of these cycles in the calving intervals following the expression of the corpus luteum or rupture of cystic follicles, but was found to be statistically different from the non-copulatory cycles preceding these conditions. There were 53 per cent of the non-copulatory cycles in the calving intervals preceding ovarian disturbance which were 27 days or less in length, as compared to 68 per cent of such cycles in cows clinically normal throughout life.

There were 52 per cent of the normal cows in which 63 per cent or more of their cycles lay between 17 and 27 days in length, whereas there were no cows in the clinically abnormal group in which 63 per cent of their cycles preceding the abnormal calving interval fell between 17 and 27 days. Hence it may be concluded that extreme variation in the length of the oestrus cycles of a cow is a presentiment of ovarian abnormality.

¹ Paper from the Department of Genetics, Agricultural Experiment Station, University of Wisconsin. No. 177. Published with the approval of the Director of the Station.