Countries in the warm climatic zones need greater domestic supplies of milk. To increase yields, the option that is least expensive and most widely used is to cross dairy breed sires with local cattle. First generation crosses have more vigor than other crosses under stressful environmental conditions; growth rate, milk yield, and reproduction rate exceed those of local breeds and other crossbred combinations. On average, lactating first generation crosses are fed energy at 45 to 60% below their potential response, which limits their capabilities. Other crosses with local breeds fall short of first generation crosses as do some of the present synthetic breeds with 5/8 to 3/4 dairy breeding. Well-fed (> 2.5 maintenance needs) Holstein or Jersey crosses containing 1/4, 1/2, or 3/4 Bos indicus (Zebu) tend to follow projections of parental means for milk yield, reproduction rate, and tolerance to heat stress; however, for crosses, losses exceed predictions for lactation length, persistency of milk yield, feed efficiency, and rate of milking. Size of thoracic and abdominal organs, size of endocrine glands, stomach weight, and intestine length are lower than expected compared with values for purebreds. The smaller digestive system affects feeding intake of B. indicus crosses, and the smaller endocrine glands appear to limit responses to high energy diets. Possible directional dominance of B. indicus needs further investigation. The first generation crosses could support their use for dairy purposes if feeding rate and management were optimal, but prospects for other crosses remain questionable.
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