Various species differ markedly in their requirements for folic acid. Young ruminants without a fully functional rumen require folic acid supplementation of milk replacer. There was no indication of folic acid deficiency in calves fed a synthetic milk containing 52 µg of folic acid per kg (23.6 mg per lb) of liquid fed at 10% of body weight (Wiese et al., 1947). In lambs 0.39 mg of folic acid per liter in milk replacer prevented deficiency (NRC, 1989). The NRC (1989) for dairy cattle recommends that milk replacer for calves should contain 0.5 mg of folic acid per kg (0.23 mg per lb). Weekly injections of 160 mg of folic acid given to dairy cows starting 45 days after breeding increased both the placental and colostral transfer of folic acid to calves, although calf performance was not affected (Girard et al., 1995). Supplemental folic acid fed at either 2 or 4 mg per kg body weight significantly increased serum folic acid concentration, but did not alter serum levels of either vitamin B12 or vitamin B6 (Girard and Matte, 1999).
The primary source of folic acid for ruminants is rumen microbial synthesis, although intestinal microbial synthesis also occurs. Certain antibiotics inhibit microbial synthesis of folic acid in both the rumen and intestine. Sulfonamides are folic acid antagonists. Mycotoxins can also inhibit microbial intestinal synthesis of folic acid in swine (Purser, 1981). Rumen folic acid synthesis is greater with high-concentrate rations than with high-forage rations (Girard et al., 1994).
Fluctuations in the concentration of serum folates observed during the first months of life of young ruminants may be an indication that synthesis of folates by ruminal microflora is not sufficient to meet requirements during weaning (Girard et al., 1989a). Girard et al. (1989a) observed that concentration of serum folic acid of calves at two weeks of age is half that of four-month-old heifers. An age effect on development of the rumen was observed, in which parenteral folic acid markedly increased serum folic acid in two-week-old heifers, while in four-month-old heifers the increase was less marked. Similarly, Dumoulin et al. (1991) observed that supplemental folic acid increased calf growth rate during the first five weeks after weaning but not thereafter, suggesting that folic acid status was marginal during the postweaning phase. In the same experiment, there was no effect of supplemental folic acid on mammary gland development of heifers (Petitclerc et al., 1999).
For adult dairy cows, Girard et al. (1989b) reported that serum folates can be increased by an intramuscular injection of folic acid, but the effect on serum and milk folates is reduced in lactating and pregnant cows. Serum folates are higher in non-gravid cows than in pregnant cows (Girard, 1998a, b). Serum folates decrease by 40% from two months postpartum until the next calving. Tremblay et al. (1991) reported that serum folates of dairy cows are lower one month prior to calving than two months after calving. These results suggest a higher folate requirement during pregnancy in dairy cows. Girard et al. (1995) also reported that apparent tissue utilization of serum folates was greater in pregnant, nonlactating dairy cows than in nonpregnant, lactating cows in early lactation. Likewise, in sheep serum, folates were significantly lower during pregnancy in breeds that give birth to larger numbers of lambs, for example, Romanov and Finnsheep more than Suffolk (Girard et al., 1996).
The effects of weekly injections of 160 mg folic acid, starting 45 days after breeding and continuing through six weeks of the next lactation, were investigated in lactating dairy cows (Girard and Matte, 1995). Parenteral folic acid supplementation tended to increase milk production and milk protein percentage in the latter half of lactation and increased milk protein percentage in multiparous cows during the first six weeks of the next lactation (Girard and Matte, 1995). In a subsequent trial, cows were fed folic acid at 0, 2 or 4 mg per kg body weight starting 30 days before calving and continuing through 305 days of lactation (Girard and Matte, 1998). In this trial, milk production was significantly increased in multiparous cows during the first 200 days of lactation, and especially during the first 100 days of lactation. Cows fed 4 mg folic acid per kg of live weight produced 6% more milk (4.8 lbs or 2.2 kg per day) than controls during the first 100 days of lactation and 10% more milk (6.6 lbs or 3 kg per day) from day 100 to day 200. Milk production of primiparous heifers fed folic acid was lower than controls during the first 100 days of lactation and not different thereafter. These results suggested a parity x stage of lactation effect on the response to supplemental folic acid. Most recently, the same researchers tested the effects of feeding 0, 3 or 6 mg folic acid per kg body weight to dairy cows fed rations either sufficient or insufficient in calculated methionine status (Girard et al., 1998). This study used only multiparous cows (n = 54), which were fed supplemental folic acid during the first 305 days of lactation. There was no effect of feeding supplemental folic acid on milk production in this trial despite higher average milk yields of cows compared to previous trials—23,800 versus 18,910 lbs (10,818 versus 8,595 kg) over 305 days.
