Abstract
The influence of age at first calving on the milk production of crossbred dairy cows produced under major dairy cattle cross-breeding prnjects in Pakistan was studied from the year 1974 to 1980. These animals were bred and rased at the Livestock Pro. cluction. Research. Institute, Bish.adurna,gar (LPRI), Livestock Experi-ment Station, Karachi (LES) and the University of Agriculture, Faisalabad (UAF). Local SahiwaI OWL) cattle were crossed with two European breeds, ililstein Friesian (11F) and Jersey (1) at LPRI and UAF. At LES, flatly* Red Sirldili (RS) wtre crossed with the HF and J breeds. At LES and UAF, the crossbrd progeny thus, produced, comprised of halibreds only -while. at LPRI. 314 HF, 3f4 J, 1/4 HP and 1/4 J groups were also available for this study, The average age at first calvitig was considerably higher arnolig the native breed'. At LES, the RS calved first at an age of approximately 56 months. Corresponding values for SWLs at LPRI. •n.d LIAF were 44 and 64 months, respectively. The 1/2 HF and 112.J crossbreds calved first at the age of approximately 25, 20. 34, 36. 37 and 38 months at LPRI, LES and UAF respectively. For 3/4 3,14 Jr, I'4 HF and 1/4 J groups of LPRI, the average age at first calving was 29, 26, 34 and 33 months. Considerable differences in age at first calving between the crossbreds and Dative breeds were observed. Due to early maturity, the former attained the peak level of milk production in third lactation whereas the latter groups. because of late maturity, reached this level in their fourth lactation. This study suggested that early maturity in Zebu cattle could be nduced through crossbreeding with Bas lams,
