Association between PTA for Feed-Saved from foreign Holstein sires and daughters’s production and reproduction traits in Isfahan Province

Introduction: The Holstein dairy industry uses several indices to evaluate feed efficiency. Feed Saved (FS) is one of the indices commonly used for this purpose. The FS index is defined as a combination of maintenance requirements, represented by the estimated breeding value for body weight, and metabolic efficiency, measured as residual feed intake (RFI). The objective of the present study was to investigate the association between sires’ predicted transmitting ability for FS (PTA (FS)) and the performance of their daughters, including production traits (305 day milk yield- MY, 305 day fat yield- FY, and 305 day protein yield- PY), a health trait (somatic cell score - SCS), and reproductive traits (days open -DO, number of inseminations per conception - NIPC, calving to first insemination interval- DFS, and age at first calving- AFC).
Materials and methods: In this study, data from 38,984 first lactation cows belonging to 81 herds, which calved between 1999 and 2024, and were collected by the Vahdat Cooperative of Agricultural and Industrial Cattle Breeders of Isfahan, were used. These cows were daughters of 432 sires, with an average of 90.24 daughters per sire, a maximum of 853, and a minimum of one daughter. After obtaining the data from the Vahdat Cooperative, the AltaGenetics website was used to retrieve sire information. By entering the semen registration number of each sire in the dairy bull search section, the corresponding sire catalog was displayed, and the PTA (FS) value was extracted from the Health Traits section and recorded in Microsoft Excel. The daughters’ performance data used in conjunction with PTA (FS) included production traits (MY, FY, and PY), a health trait (SCS), and reproductive traits (DO, NIPC, DFS and AFC). Data editing was performed using R software (version 4.5.2). Descriptive statistics and correlation coefficients for the studied traits were also calculated using this software. The association between daughters’ performance and sires’ PTA (FS) was analyzed using a linear mixed model implemented in the lmerTest package of R. In this statistical model, herd, year, and season of calving (HYS) were considered as fixed effects; PTA (FS) and AFC as covariates; and cow as a random effect. The genetic trend was estimated by regressing PTA (FS) on year of calving.
Results and Discussion: The correlations between sire PTA (FS) and daughters’ performance were in the range of 0 to 0.03 for production traits and –0.01 to 0.03 for reproductive traits. The regression coefficients of daughters’ MY, NIPC, and AFC on their sires’ PTA (FS) were –1.36 kg, –0.00007, and –0.03 days, respectively (P < 0.01). The estimated regression coefficients for FY, PY, SCS, DO, and DFS were not statistically significant (P>0.05). The genetic trend (-2.30 lb/yr) for sires PTA (FS) was not significant (P > 0.05). The minimum, maximum, and average values of PTA (FS) for Holstein sires in Isfahan were –483, 674, and 73.42 lb, respectively.
Conclusions: The results indicated that the range of the FS trait among sires of dairy cows in Isfahan province was very wide. In other words, due to the diversity of available Holstein semen and the ease of access to these semen sources in the country, a large number of different sires can be used even within a small herd. Consequently, these semen resources can be utilized to achieve various breeding objectives. The mean values of MY and PY, as well as some reproductive traits (NIPC and AFC), were lower in the group with positive FS compared with the group with negative FS. The results suggest that this important trait reported in Holstein sire catalogs can be used to improve feed efficiency, which represents one of the most costly components in dairy cattle production.