Abstract
Reproductive data, such as numbers of days to the first estrus and A.I. service postpartum, number of days to conception, number of A.I. services required for conception, interval between the first estrus and first A.I. service and the average interval of A.I. service in Thai native-Friesian crossbred and pure Friesian dairy cows, were compiled in the National Dairy Training and Applied Research Institute in Chiang Mai, Thailand. The data were analyzed statistically and the effect of milk production on these reproductive traits was investigated. The reproductive efficiency of purebred cows was obviously inferior when compared with crossbred animals, in spite of special care being given to the purebred only in order to alleviate the effect of a tropical climate and provide better feeding. However, the regression analysis between reproductive and lactational parameters revealed a definite antagonistic effect of lactation on reproduction, especially in the purebred cows, which had a larger amount of milk production and longer lactation period. If these effects of lactation were eliminated, there would be no evident difference in reproductive efficiency between purebred and crossbred cows in the conditions of this study. Among the reproductive parameters examined, the number of days to the first estrus and interval between the first estrus and first A.I. service were less affected by breed difference and the magnitude of lactation than other reasons. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 8 : 1093-1101)
Highlights
The main body of dairy cattle kept in northernThailand are crossbreds of various degrees between Thainative and Friesian cows
In the farm at National Dairy Training and Applied Research Institute (NDTARI), the crossbred between Friesian and Thai natives and the pure Friesian cattle were kept in different herds
Data collected in cross- and purebred Friesian cows are summarized in Table 1, records of milk performance in previous lactations were omitted from the table because of the absence of obvious relationships between them and reproductive performance in current lactation (See the section)
Summary
The main body of dairy cattle kept in northernThailand are crossbreds of various degrees between Thainative and Friesian cows. Crossbred and purebred Friesian cows, respectively, fed in the National Dairy Training and Applied Research Institute (NDTARI), Livestock Department, Ministry of Agriculture, in Chiang Mai. We analyzed the effect of a tropical climate on their lactations. A lot of work has been done on the antagonistic relationship between milk production and reproductive performance of dairy cattle over many years since the pioneer work of Gaines (1927). The analyses performed on a large scale in recent years were all agreed in recognizing the adverse effect of increased milk yield on the fertility of cows, which was expressed in terms of number of days open, calving interval and so on
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