Joosten, I., Van Eldik, P., Elving, L. and Van der Mey, G.J.W., 1987. Factors related to the etiology of retained placenta in dairy cattle. Anim. Reprod. Sci., Birth records of 369 288 calvings of 160 188 Meuse-Rhine-Yssel cows were analysed to assess the influence of factors associated with retained placenta. Special emphasis was placed on the analysis of a subset containing data on births involving a single live calf and an easy or normal calving process. The overall rate of incidence of retained placenta was 6.6%. The rate increased during the years studied. Abortion, stillbirth and multiple birth caused a marked increase in rate, as did difficult calving, caesarean section and fetotomy. After adjusting for these factors, analysis of the corrected subset showed that the rate of incidence increased with age of the dam. Gestation length prior to retention and birth weight were also associated with higher rates. The combination of short gestation length ( < 270 days) and low birth weight ( < 37 kg) was associated with the highest risk of retained placenta. High birth weights mainly caused higher rates when related to dystocia. The incidence rate in cows delivering a male calf was only slightly higher than in cows delivering a female calf. Cows having retained placenta for a first or second time were three and six times, respectively, as likely to do so again at a subsequent parturition when compared with cows which had not had retained placenta previously.

The mean gestation periods of mares belonging to different horse and pony breeds common in The Netherlands have been calculated using data from the birth registers of five stud-book societies. The following mean values have been determined: Fjord pony: 342.2; Haflinger pony: 341.3; Draught horse: 343.3; Shetland pony: 337.2; and Frisian horse: 337.7 days. The variation in the mean gestation period is greater in horses than in cows, sheep or pigs. Colts are carried a little longer than fillies. Differences between years are not significant, but differences between the various breeds have been determined. Shetland foals born before 1 June are carried longer than those born after 1 June. The gestation period for mares of this breed mated at 2 years, is significantly longer than for those mated at more than 2 years.The length of the gestation period in horses is possibly affected by physiological factors other than those influencing the gestation period in some other farm animals.

A breeding experiment was carried out in a group of Shetland ponies in order to investigate the heredity of congenital lateral patellar (sub)luxation. A breeding herd was established and consisted of stallions and mares acquired at different times. Some were free from, and others were affected by lateral patellar (sub)luxation in either one or both femoropatellar joints. Over a period of 20 years, 49 foals were born from different mating combinations. Some offspring were free from the defect and others showed the abnormality. Though the number of foals bred during the experiment is rather small, there is sufficient evidence to suggest a monogenic autosomal recessive hereditary transmission of the defect.

No abstract

No abstract