Abstract
In order to measure the influence of the temperature-humidity index (THI) and the variation of fat thickness on reproductive performance, ninety-two Bos indicus cows kept under grazing conditions were used in two farms in Veracruz (Mexico) and Puntarenas (Costa Rica). THI was calculated with the average environmental temperature and relative humidity. Measurements of fat thickness (FAT) were taken two weeks apart from the last trimester of gestation to approximately 80 days postpartum (dpp). Natural breeding was used in both farms. Time to conception was calculated based on the interval from days at risk to conception (DRC), which had to be at least 28 dpp. THI was between 65.4 ± 2.9 and 73.2 ± 1.5 in Veracruz and 75.4 ± 0.26 and 76.5 ± 0.55 in Puntarenas. Variations in THI were observed in Puntarenas whereas in Veracruz THI variations were more prominent. In Veracruz, loss of fat during the last trimester of gestation was on average 8.5%, whereas in the postpartum period it was 18.4% (P = 0.042). In Puntarenas, the variation in the last trimester of gestation was on average 18.7% and in the postpartum period was 10.5% (P = 0.012). The relative change in FAT in Veracruz was 36.7%, and in Puntarenas it was 29.3%. Overall, 60% of the cows became pregnant. FAT decreased the interval of DRC (R2=0.06; P=0.033) with a high relationship (R2=0.76; P< 0.0001) between THI and time to conception, in both farms. In conclusion, THI levels influence the reproductive performance in early postpartum period affecting DRC.
Highlights
The effect of the environment on productive and reproductive activities has been the subject of much study [1,2,3,4,5]
The study was carried out from February to August 2015. Both farms are located in the zone considered as dry tropics (National Institute of Statistic and Geography, http://www.inegi.org.mx; National Meteorological Institute of Costa Rica, http://www.imn.ac.cr.) The temperature-humidity index (THI) for each farm was calculated monthly considering the average environmental temperature and relative humidity of the period in which the study was conducted, applying the equation proposed by Garcıa-Ispierto et al [16]: THI
This causes the dam to mobilize body energy reserves, which triggers negative energy balance [20]. This was confirmed in the present study, since the animals from the farm in Veracruz had greater back fat thickness loss during the postpartum period as opposed to the prepartum period (P = 0.042)
Summary
The effect of the environment on productive and reproductive activities has been the subject of much study [1,2,3,4,5]. Stress in cattle due to the harsh environmental conditions has several effects on reproductive physiology, such as the presence of overt signs of estrus, rate of ovulation, and embryo survival [2, 6]. Villa-Mancera et al [7], reported a direct effect of the temperature-humidity index (THI) on conception rate, registering lower levels of fertility during the summer months compared to the winter. It is well-known that Bos indicus cattle raised under tropical conditions show prolonged calving intervals [8, 9], which are attributed to long periods of postpartum anestrus [10].
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