Production performance
Animals those completed nine parities, four periods and, three seasons were considered for studying the production and reproduction traits. The least square means of productive traits is shown in Table 1. The overall least square means for 305 DLMY was 1019.83±29.22 kg, while
Gaur et al., (2002) reported lesser values than present study. The total LMY for Ongole cows was 1063.33±31.13 kg, which is much higher than the earlier reports of
Gaur et al., (2002), Singh et al., (2008), Kumar et al., (2016) in Ongole cows. The present study showed that parity and period were significantly (P<0.01) affecting the 305 DLMY and total LMY, whereas the season had no effect on the two traits. Our study concluded that there is progressive increase of total LMY and 305 DLMY from 1st parity to 8th parity. Animals calved in period four were given highest milk (Fig 1) compared with other periods which may be due to progressive improvement in management of the farm over the time. The overall LL in Ongole cattle under study was 266.26±5.6 days. But lesser LL was reported by
Singh et al., (2008) and
Kumar et al., (2016) in Ongole cattle. Highly significant (P<0.01) effect of parity was observed on LL whereas the effect of period and season were non-significant. The least square mean PY was 4.82 ±1.03 kgs. This is much higher value as compared to the peak yield reported by
Gaur et al., (2002), Singh et al., (2008) and
Kumar et al., (2016) in Ongole cattle. The parity and period had significant effect (P<0.01 and P<0.05 respectively), season didn’t influence PY.
Reproduction performance
The least squares means of various reproductive traits is shown in Table 2. The mean AFS and AFC recorded in this study was 1273.89±38.87 days and 1572.61±34.69 days, respectively. The AFC is almost similar to the reports of
Gaur et al., (2002) but higher than the reports of
Kumar et al., (2016) in Ongole cattle. Period and season were non-significant on both the traits. The overall CI recorded in this study was 497.95±8.58 days, which is almost similar to the CI reported by
Singh et al., (2008), lesser than the values reported by
Kumar et al., (2016) in Ongole cattle. The parity and the period were affecting the CI significantly (P<0.01) but season had no influence. The highly significant effect of parity and period on CI of Ongole cattle may be attributed to the physiological stability and improved set of management practices over the time. The SP and the DP recorded in present study are 188.19±5.17 and 214.79±19.6 days, respectively. These values are lower than the reports of
Gaur et al., (2002), Kumar et al., (2016) in Ongole cattle. The parity, period and season didn’t influence the SP and DP.
Heritability
Hertitability of various traits studied were presented in Table 3. The Heritability estimates for 305 DLMY yield was 0.40±0.16, which is higher than the reports of
Singh et al., (2020). The total LMY was moderate (0.31± 0.14) which is higher than the reports of
Singh et al., (2008) and
Vinoo et al., (2005) in Ongole cattle. Such differences in the heritability estimates are expected and are mainly results of size of dataset, genetic variation within population, management and environmental conditions and the methods used for parameter estimation
(Wondossen et al., 2017). Moderate heritability for LMY and 305 DLMY indicates that still there is an opportunity for improving these traits through selection, future improvement of the herd could be meaningful if the selection of animals based on genetic merit combined with improved herd management as well as introduction of new animals from other source to increase genetic variability within the herd. The heritability estimates for PY was 0.10±0.08 and LL had low heritability estimate (0.05±0.07). These observations are in accordance with reports of
Kumar et al., (2016) in Ongole cattle. However,
Singh et al., (2008) and
Vinoo et al., (2005) reported medium heritability estimate of LL in Ongole cattle. The heritability estimate for AFC was 0.10±0.16, the current estimates were comparable with the estimates of
Kumar et al., (2016), Vinoo et al., (2005) in Ongole cows. Heritability of SP was 0.11±0.09.
Kumar et al., (2016) and
Vinoo et al., (2005) also reported similar heritability for SP in Ongole. The result reflected that the SP at the farm may further be improved successfully by improving feeding and management including heat detection, artificial insemination and pregnancy diagnosis. DP had low heritability (0.16±0.02). Heritability of CI was low (0.23±0.02).
Kumar et al., (2016) and
Mishra et al., (2018) reported lower heritability values than present study. This relatively low heritability estimates for CI could be explained by large environmental variance. Therefore, improvements in nutrition and reproductive management should lead to a considerable decrease in length of CI than making purely genetic selection alone.
Correlation
Phenotypic and Genetic correlations between milk production traits were high in the present study. The genetic correlation observed between LMY and 305 DLMY was positive (0.74±0.03) and highly significant (Table 3). This means that genetic improvement of one milk production trait could result in a correlated response in the correlated trait. Generally, the very high correlation between these two traits is indicative of the fact that using 305 DLMY can be sufficient to meet selection for lactation milk yield
(Wondossen et al., 2017). This is comparable with results of
Ahmad et al., (2001) and
Singh et al., (2008). The highest genetic correlation between milk productions traits is the result of pleiotropy
(Falconer, 1996).
Lactation milk yield had high genetic and phenotypic correlation with PY (P<0.01) and LL(P<0.05). Similar relationships between total LMY and LL were reported by
Vinoo et al., (2005) and
Kumar et al., (2016). The PY had significant genetic and phenotypic correlation with LL.
Singh et al., (2008) also observed high genetic and phenotypic correlation between PY and LL in Ongole cows. Highly significant genetic correlation was found between SP and CI in the present study. Similar relationship was also found by
Vinoo et al., (2005) and
Kumar et al., (2016) in Ongole cows. The DP had positive and significant genetic correlation with the CI. Similar relationships were also observed by
Vinoo et al., (2005) and
Kumar et al., (2016). The SP had low phenotypic and moderate genetic correlation with the DP. However,
Kumar et al., (2016) found high genetic and phenotypic correlation between the SP and the DP in Ongole cows. This positive genetic correlation among the reproductive traits in the present study suggest that improvement of one reproductive trait will have positive impact on the other reproductive trait. Negative correlation was observed between production traits and the SP and the DP, suggesting while selecting animals for milk production, threshold levels of the SP and DP are to be given due consideration. Positive genetic correlations observed among 305 LMY, total LMY, PY and LL with CI, indicating cows with high milk yield have longer calving intervals. Environmental correlations among production traits ranged from 0.61 to 0.91 and for reproduction traits -0.10 to 0.64.
