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The twinning rate in a herd of Holstein dairy cattle and its effect on lactation and calf performance was investigated by using records of 5815 calving events. Data from twin calving Holstein cows in (TEC-DAP) farm in Al-Fayum Governorate between January 1997 and April 2008 were compared to those giving singles to study the differences in subsequent milk yield, previous and subsequent lactation and dry period length, as well as calf performance. The obtained average twinning rate was 1.4% during the period of the study. Cows giving twins had a significantly (p<0.01) lower daily, peak and 305-d milk yields than those with singles. There was no significant difference (p>0.05) in previous and subsequent lactation and dry period length between cows calving twins or singles. Calves born as twins were significantly (p<0.005) lighter at birth and weaning time than single calves, whereas total birth weight and total weaning weight were significantly (p<0.005) increased for twins than singles. Daily body weight gain from birth to weaning was significantly lower (p<0.005) for twin than single calves. Twinning in dairy cattle has a negative depressive effect on subsequent milk yield. Calf weight produced at weaning per cow calving can be increased in cows producing twins relative to cows producing singles. Alleviation of twinning constraints including dystocia, reduced calf survival and low reproductive performance requires improved management practices and early diagnosis of cows gestating twins in order to provide higher nutritive requirements in the last trimester of gestation and proper timing of drying off, and for higher assistance requirements at parturition. Thus, due to the increased disadvantages which did not offset the additional returns earned by calves, twinning in dairy cattle via selection or artificial induction appears not to be desirable.  The twinning rate in dairy cattle seems to have increased recently, and this may have important practical implications (Kinsel et al., 1998). The regulation of ovulation rate appears to be the primary mechanism for regulating litter size (Wiltbank et al., 2000). A number of factors were identified as possible regulators of twinning rates including age of dam (Jones and Rouse, 1920; Fricke and Wiltbank, 1999; Wiltbank et al., 2000), season (Cole and Rodolf, 1924) and genetics (Lush, 1925). Other factors have been found to be associated with twinning, including use of antibiotics or reproductive hormones, ovarian cysts, days open, and peak milk production (Pfau et al., 1948; Johansson et al., 1974; Nielen et al., 1989; Ryan and Boland, 1991; Lopez-Gatius et al., 1996; Kinsel et al., 1998; Wiltbank et al., 2000).Studies of the effects of twin births on milk production in the subsequent lactation are contradictory. Cows with twins had greater milk production than cows with singletons (Auran, 1974; Syrstad, 1974; Wood, 1975; Kay, 1978; Wood, 1984; Eddy et al., 1991) while in others lower milk yields were recorded (Bar-Anan and Bowman, 1974; Suchanek, 1977; Syrstad, 1977; Chapin and Van Vleck, 1980). Effect of twinning on birth weight, weaning weight and growth of calves has been investigated in several studies (Bellows et al., 1971; Turman et al., 1971; Bellows et al., 1974; Johansson et al., 1974; Davis et al., 1989; Gregory et al., 1990, 1996; Echternkamp and Gregory, 2002; Bell and Roberts, 2007). The aim of this study included the determination of twinning rate in a Holstein dairy cattle herd and investigation of its effect on milk yield, lactation length, dry period length and calf performance.

Twinning in dairy cattle and its effect on milk yield, lactation length, dry period length and calf performance