Author: Amy MowreyPublisher:
ISBN:
Category : Dairy cattle
Languages : en
Pages : 190
Book Description
Historically speaking, fertility has decreased and milk yield has increased in modern dairy cows. This has led to a large amount of research focusing on increasing pregnancy rate in lactating cows. Some believe that an increase in nutrients fed to early lactation dairy cows is required for high milk production and reproductive function. To test this hypothesis researchers have tried to increase the energy density of the diet or to feed different types of fat (an energy dense nutrient). Three experiments were conducted to test the effects of type and amount of fat fed to lactating dairy cows on fermentation, production and reproductive function. The first experiment compared a control diet (no supplemental fat) to type of raw soybean (cracked or ground) and a rumen inert fat source. Each diet was fed to four rumen-cannulated midlactation dairy cows. The only fermentation parameter affected by diet was the solids passage rate, which decreased for the cracked soybean diet. Reproductive parameters were unchanged by dietary treatments. The second set of experiments tested these diets and others for a longer period of time using more animals. One hundred and fifty-two early lactation dairy cows were fed different levels of fat in a study completed over two years (Year One (Y1) n 84; Year Two (Y2) n = 68). Year One cows were fed a control diet, one with added soybeans, or one containing a rumen-inert fat product. Pretreatment and experimental milk yield were significantly higher for cows fed the control and soybean diets. This was due to random assignment of lower BW cows to the treatment containing the rumen inert fat product. We concluded that no difference due to treatment occurred but instead the difference was due to BW differences. During Y2 cows were fed a control diet or three diets increasing in soybean content. Milk protein percentage decreased as soybeans were added to the diet. Other production parameters were similar across treatments. Plasma cholesterol at week 10 of lactation and amount of total fatty acids in plasma increased with increasing soybean content. Number of estrous cycles for cows fed the lowest soybean diet during Y2 was the only significant change in the reproductive parameters measured for both years. In summary, early lactation dairy cows maintained intake and milk production levels similar to control cows when fed supplemental fat, after taking BW into account. Small changes were noted in plasma fatty acid content and cholesterol during Y2, but these increases were not translated into increases in progesterone concentration or changes in reproductive efficiency or function.
