Abstract
The backfat thickness (BFT) was used to forecast the onset of ovarian activity and predict the calf growth. Eighty Brahman cows with their calves were allocated in two groups of 40 distributed in 4 months according to the month of calving, starting in March and finishing in June. One was synchronized and inseminated at fixed time following by natural mating (TAI+NM); whilst the other only by natural mating (NM). The programs started at 60 ± 5 days postpartum and ended 60 days later. From day 30 postpartum, serial ultrasound examinations and progesterone samples were used to monitor the onset of ovarian activity. The BFT in the rump area was measured by ultrasound from 30 days postpartum and every 15 days thereafter. The weight of the calves was recorded at birth and at weaning on 160 days. The adjusted effect of BFT on ovarian activity and the calves' development was assessed by binomial logistic regression at 30, 60, 75, and 120 days postpartum. The cycling cows averaged higher BFT irrespective of breeding program (P < 0.001). Also, slower changes in BFT were recorded during the follow-up at each time for all cows. However, the former had the higher BFT values from calving to the end of the study (P < 0.001). At 60, 75, and 120 days, the BFT measured, at the preceding time, was the only factor predicting the commencement of cyclicity (P < 0.001). The accumulative pregnancy through time was higher in TAI+NM (P = 0.003). Daily weight gain and weaning weight of the calves born in March was significantly heavier (P < 0.001) than peers born in April, May, or June. The most critical element to forecast the onset of ovarian activity is the monitoring of BFT around calving regardless of the breeding program. BFT to estimate the development of the calves until weaning was unpredictable.
Highlights
The restoration of ovarian activity in Zebu cattle is commonly affected by the availability and quality of native or introduced pastures
These features are dependent on the onset of the rainy season, that can be unpredictable in many areas of the tropical world [1]
Ultrasonographic measurements of backfat thickness (BFT) is a tool allowing us to obtain an objective measure of the animal current metabolic state, especially in the last trimester of gestation, when other indicators such as weight, body condition score, glucose, nonesterified fatty acids (NEFA’s), among others, become difficult to interpret [2, 5, 6]
Summary
The restoration of ovarian activity in Zebu cattle is commonly affected by the availability and quality of native or introduced pastures. Ultrasonographic measurements of backfat thickness (BFT) is a tool allowing us to obtain an objective measure of the animal current metabolic state, especially in the last trimester of gestation, when other indicators such as weight, body condition score, glucose, nonesterified fatty acids (NEFA’s), among others, become difficult to interpret [2, 5, 6]. This methodology is not frequently used in breeding programs for predicting the early resumption of ovarian activity postpartum. The development of the calves in the tropics can add useful information in the decision-making process as to decide on the most adequate time to breed animals [7]
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