GENETIC ANALYSIS OF THE RELATIONSHIP AMONG TEST-DAY MILK YIELD, SOMATIC CELL COUNT AND SOME UDDER CHARACTERISTICS OF HOLSTEIN FRIESIAN COWS

Abstract

Genetic analysis of the relationship between test-day milk yield (TDM), somatic cell count and score (SCC&SCS) and ten udder-teat traits of Holstein Friesian cows was carried out using multi-trait animal model package. A total number of 3909 observations were collected on 2811 cows raised in four Egyptian dairy farms. Estimates of h 2 TDM ranged from 0.28 to 0.34, h 2 TDM increased markedly with advancing parity till the 3 rd lactation, and varied according to stage of lactation ranging between 0.14 and 0.23. Overall h 2 SCS for all parities was 0.19. The highest h 2 SCS was obtained in the 1 st parity whereas estimates of latter parities were obviously lower. Results indicated no clear effect of stage of lactation on h 2 SCS. Estimates of h 2 for udder and teat traits ranged from .29 to .54 and .46 to .61, respectively. Thus selection based on udder and teat measurements would be effective to improve these traits. Estimated correlation coefficients indicated a negative association between TDM and SCS. Genetic (rg) and phenotypic (rp) correlations among TDM and SCS showed generally low to intermediate values ranged from -.08 to -.28. There was a general trend towards slight increase in magnitude of RgTDM*SCC with advancing parity. This result may suggest that as SCC in milk increased, milk production will be in turn decreased, as a result of probable mastitis infected udder. Both rear udder width (RUW) and udder cleft (UC) showed genetically the highest positive association with TDM. This may indicate the possibility of indirect genetic improvement of TDM by selection for both RUW and UC. Estimates of RpSCS with udder traits were all negative, indicating that cows with higher, more tightly attached udders and closer teats have lower SCS. RgTDM with some udder-teat traits were positive and showed a general tendency towards increasing their magnitude with advancing parity. Other udder and teat traits showed, however, negative Rg with TDM and become greater in magnitude with advance in parity except with fore udder attachment (FUA). Udder depth showed the highest negative Rp (-.55) with TDM in the 4 th lactation. Fore udder length (FUL) showed moderate positive Rp with TDM indicating that cows with longer fore-udders tend to produce more daily milk yield. For the other udder traits, particularly teat size (TS), the estimates of Rp with TDM were moderate and favorable and showed a tendency to increase in magnitude with parity. Genetic parameters for all studied traits are possible aids for constructing selection indices for improving udder health and milk yield.