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Acta sci. vet. (Impr.); 40(1): Pub. 1017, 2012. tab

Artigo em Português | VETINDEX | ID: biblio-1373524

Resumo

Background: The need for high production has increased considerably in the dairy industry. On the other hand, a fertility decline has been observed in cows with best potential for milk production. Therefore, calving intervals of around 12 months have been sought, which leaves a very short period of time for the cows to be inseminated and to become pregnant. If the conception is delayed, the reproduction inefficiency can reduce milk production, causing economic problems. The calving-conception interval (CCI) depends on multiple factors such as voluntary waiting period, insemination technique, birth season, herd size and parity. Negative effects of stress caused by heat on the fertility of lactating dairy cows have been observed. An increase in body temperature decreased the probability of conception at 28 days as the number of postpartum days increased. It is known that cows with larger calving-conception intervals have more health problems. Also, they have a greater chance of being discarded, since long CCI result in longer periods with no milk production and, therefore, expenditures with unproductive cows. Moreover, an increase in the CCI from 90 to 300 days doubled the chance of discard or peripartum death in dairy matrix. This study aimed to analyze the effect of two variables: the calving - first IA interval and on the CCI of crossbred dairy cows: duration of previous calving interval and calving season. Materials, Methods & Results: Data were collected at a property located in the state of Goiás, Brazil, between 2009 and 2010, for a herd of 71 crossbred cows with an average production of 1,400 kg of milk per day. Cows were artificially inseminated and pregnancy diagnosis was performed monthly using ultrasonography (Mindray DP3.300® VET). The previous calving interval was evaluated in three subdivisions: 1 (300 365 days) 2 (366 500 days) 3 (above 500 days) and birth season was classified as spring-summer and autumn-winter. The calving-first IA interval and the CCI were analyzed by ANOVA in MINITAB. The effects of previous calving interval and birth season were included in the model. There was no effect of duration of either previous calving interval or calving season on the calving - first IA interval, but the birth season variable affected the CCI. Cows that calved in autumn/winter had a lower CCI when compared with calving in spring/summer (80.17 d. vs. 118.50 d). Discussion: In hot summers the conception rate is lower among cows that deliver during summer and spring when compared with those that deliver during autumn and winter [4]. Other authors have shown that conception during summer was, respectively, 25 to 30% and 36% lower than during winter. Although the length of the previous birth interval did not influence the calving-conception interval, herds with average CPI greater than 13.9 months had a 1.78 times higher risk of death than herds with average CPI smaller than 13 months. In addition, the risk of cows being discarded increased due to a decline in milk production for CCI greater than 15 months. This is particularly an issue for crossbred herds due to their low lactation persistence. The CCI was significantly influenced by the calving season and it was also influenced the CCI in Gir cows in the Northeast Brazil that had calving interval of 460 +9.4 days when they that calved in spring/summer and 430.8 +9.5 days when they calved in autumn/winter. The effect of the calving season on the service period has been explained as a result of poorer feeding conditions at certain times of the year for purebreds. Other authors contradict these results, but they investigated Nelore cows, showing the adaptation of this breed in subtropical climates.

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