Heritability estimates of early lactation traits and lifetime traits
Heritability of early lactation traits was low ranging from 0.06±0.04 for DP and 0.06±0.01 for LL to 0.38±0.08 for birth weight (Table 1). The estimated low heritability for these traits indicated limited role of genes and these traits are more under environmental control and can be influenced to a great extent by management practices followed at the farm. The low heritability of lactation length may be due to several factors such as differences in total records, number of records per animal, data editing and statistical model
(Du et al., 2020). The lower heritability estimate for the lactation length was also reported by
Choudhary et al., (2003) in Sahiwal cattle as 0.132±0.131 ,
Dash et al., (2018) in Karan Fries cattle as 0.11±0.05 and
Singh et al., (2020). However, moderate heritability estimate for the LL was observed by
Narwaria et al., (2015) as 0.22±0.07 and
Dash et al., (2023) as 0.29±0.05 in Sahiwal cattle. Similarly, the low estimate of heritability for the dry period was observed by
Ulutaş and Sezer (2009) in Simmental cattle 0.04±0.70).
The heritability estimates for lifetime milk yield ranging from 0.33±0.07 for MYPDPL3 to 0.44±0.10 for MYPDTL5 (Table 1). The moderate heritability estimates may be due to large population size and randomization of environmental effects and indicate that these traits are under influence of additive genetic variance and further improvement in these traits can be carried out by using appropriate selection criteria.
Ambhore et al., (2017) estimated the heritabilities of LTMY3, LTMY4 and actual lifetime milk yield (ALTMY), Productive life and herd life as 0.41±0.26, 0.47±0.06, 0.43±0.05, 0.14±0.16 and 0.12±0.05, respectively in Phule Triveni cattle. Similarly,
Reddy et al., (2012) reported even higher heritability (0.66) for lifetime milk yield in Ongole cattle. However,
Jairath et al., (1994) in Canadian Holstein reported lower heritability estimates for lifetime milk yield, productive life and milk yield per day of productive life as 0.13, 0.08 and 0.32, respectively. Moderate heritability estimates for milk yield was also reported by
Tamer et al., (2017) in Holstein cows (0.33±0.02) of Egypt and
Choudhary et al., (2003) in Sahiwal cattle (0.274±0.173). However,
Singh et al., (2015) and
Ankuya et al., (2016) reported the higher heritability estimates in crossbred cattle (0.43±0.14) and Kankrej cattle (0.45±0.17), respectively.
Genetic and phenotypic correlations between early lactation traits
The genetic correlations were estimated between early lactation traits and lifetime traits (Table 1). The genetic correlation between birth weight and firstlactation length was negative. Usually, it is assumed that the calves with high BW grow well and attain maturity early. However, the calves with lower birth weight over a period of time makeup their growth and attain the maturity similar to the calves with higher body weight. Also, a long-time gap in the birth weight and expression of a particular trait also nullifies the effect if any. The low phenotypic correlation between second lactation length and birth weight might be due to factors like effect of management and environment on these traits.
Deb et al., (2005) reported that there was low correlation of BW with first lactation length (0.065) in local cow, Friesian cow x Local (0.015) and Jersey x Local (0.076).
The moderate genetic and phenotypic correlation between most of the lactation length and lactation milk yield indicated that both these traits share some common genes between them and performing selection on the basis of one trait will increase the genetic values of other trait. Relatively higher estimates of the genetic and phenotypic correlation between the lactation length and lactation milk yield was obtained by
Choudhary et al., (2003) as 0.722±0.260 and 0.674 ± 0.044 in Sahiwal cattle. However,
Banik and Gandhi (2010) in Sahiwal cattle reported low genetic and phenotypic correlation (0.029 and 0.013) between lactation length and LMY.
The estimated genetic and phenotypic correlation between first lactation length and first dry period was -0.22±0.44. and 0.01±0.04. It is the known fact that when the lactation length increased due to infertility or high milk yield reason, the dry period between the two lactations got decreased. The positive but low phenotypic correlation between the lactation length and dry period indicated that the dry period might be increased by negligence in managemental practices. Similar results were reported by
Ulutaş and Sezer (2009) in Simmental cattle (-0.05±0.112 and -0.17±0.293) and
Banik and Gandhi (2010) in Sahiwal cattle (-0.016 and -0. 002.The genetic correlation between LMY1withDP1 was -0.39±0.33. The present findings indicated that the decrease in dry period leads to increase in lactation milk yield due to increase in the number of lactation days. Similar trend was observed for phenotypic correlation between lactation milk yield and dry period (-0.08±0.05). It means that the other managemental practices of the farm were up to the mark as no further increase in dry period was observed. The result obtained in the present study was in agreement with
Dev and Dahiya (2018) in crossbred cattle (-0.62±0.23 and -0.40±0.02) and
Choudhary et al., (2019) in Tharparkar cattle (-0.928±0.32 and -0.33±0.05). Similarly,
Godara et al., (2015) reported the negative genetic correlation of dry period with age at first calving, calving interval, first lactation milk yield etc in murrah buffalo.
Genetic and phenotypic correlations between early lactation traits and lifetime traits
The moderate to high positive genetic correlation was observed between lactation length and lifetime production traits up to fifth lactation. However, the phenotypic correlations between firstlactation lengths, second lactation length and lifetime production traits up to lactation three and lactation five was found negative to low. The overall genetic correlations were found to be higher than phenotypic correlation for first lactation length, second lactation length and lifetime traits. Similar results were obtained by
Tamboli et al., (2021) in Nili Ravi buffaloes. It was observed that there was strong positive genetic correlation between the first two lactation milk yields with the lifetime traits. The results indicated that if the milk yield is high in the first two lactations the lifetime milk yield will be more. The strong positive (nearly equal to one) correlation between the second lactation milk yield and lifetime milk yield suggested that the second lactation milk yield may be considered as criteria for the selection of Frieswal cattle for lifetime milk production.
The phenotypic correlation between first two lactation milk yield with lifetime milk yield traits up to three lactations and five lactations were found to be high. The positive and high phenotypic correlation offers the scope for effective selection for the trait based on its phenotype, which would improve the other correlated traits automatically. The overall genetic correlations were found to be high than the phenotypic correlation.
Abbas et al., (2010) in Sahiwal cows reported the estimate of genetic and phenotypic correlation between first lactation milk yield and lifetime milk yield, productive life and herd life as 0.646±0.09, 0.073±0.15, 0.038±0.16 and 0.654, 0.02, 0.019, while
Kharat et al., (2009) showed very high and significant correlation of first lactation milk yield with lifetime milk yield (0.99) in Holstein Friesian crossbred cows.
Lodhi et al., (2016) estimated the genetic and phenotypic correlations between first lactation milk yield and lifetime milk yield as 0.125±0.19 and 0.252±0.03 and between first lactation milk yield and lifetime lactation length as 0.156±0.19 and 0.132 ±0.03, respectively in crossbred cattle. The negative genetic correlations between DP and lifetime traits indicate that reduced dry period has positive impact on lifetime milk yield due to more lactation days. The results of present investigation are in line with
Abbas et al., (2010) in Sahiwal cows who reported genetic and phenotypic correlation between first dry period and lifetime milk yield as 0.193±0.15.
Lodhi et al., (2016) estimated the genetic and phenotypic correlations between first dry period and lifetime milk yield as -0.136±0.21 and-0.098±0.028 and between first dry period and lifetime lactation length as -.082±0.21 and -0.119±0.028, respectively.
Genetic and phenotypic correlation between lifetime traits
It was observed that there was strong positive genetic and phenotypic correlation between the lifetime traits under study. The positive and high correlation between these traits indicated that the selection of the later traits based on the performance of early expressed trait would be highly effective and recommended for improvement through their correlated response. Similar reports were observed by
Chauhan et al., (1993) reported high genetic correlation between lifetime milk yield and herd life, productive life and total number of lactation (ranging from 0.94 to 0.97) whereas the phenotypic correlation between the lifetime milk yield and herd life, productive life and total number of lactations was moderate to high (ranging from 0.2 to 0.7).
Ambhore et al., (2017) also reported moderate to high genetic correlation with herd life and productive life (0.90 and 0.92) in Phule Triveni cattle. The genetic and phenotypic correlation between LTMY3, LTMY4 and ALTMY was found to be moderate (ranging between 0.42 to 0.47 and 0.28 to 0.52).
Thus, Lifetime milk yield is a comprehensive metric trait that combines productivity, efficiency and sustainability. While improving lifetime yield has significant benefits, it must be pursued carefully to balance productivity with animal health and welfare. Integrating genetic advancements with excellent management practices is the key to optimizing lifetime milk yield without adverse consequences.