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Beta-carotene and milk yields

Nutritional management to optimize milk yields in dairy cows involves many possible variables, including advances in feeding management and the most recent findings on individual nutrients. This point was made once again in work by University of Florida scientists (Arechiga et al., 1998), who reported significantly increased milk production in dairy cows receiving supplemental beta-carotene during early lactation.

In this large, three-part study using intensive management, the supplemented cows produced from 6.2 to 11.3 percent more milk than the unsupplemented controls. Two of the experiments took place from summer into fall--one on a southern Florida dairy and the other on a dairy in the northern part of the state. The third was a winter-spring experiment (February 1 through May 1) on the southern Florida farm to determine if there was any interaction between heat stress and milk yield with beta-carotene supplementation.

All 701 cows in the study were fed the farms' standard total mixed rations (TMR), received bovine somatotropin (BST) and were milked three times per day. The control group received no beta-carotene supplementation, while the supplemented group's ration provided an additional 400 mg of beta-carotene per head daily. All rations were also supplemented with 200,000 to 250,000 IU of vitamin A per cow daily.

The cows were generally assigned to the control or treatment group about 15 to 20 days after calving. Because calving occurred throughout the set period of each experiment, the length of beta-carotene supplementation varied by animal, but minimum supplementation was 15 days. The maximum length of supplementation was 97 days in the first experiment, 61 days in the second, and 90 days in the third.

When the researchers calculated cumulative milk yields to the last test day, the supplemented cows produced significantly more milk than the controls in Experiments 1 and 3, and numerically more milk in Experiment 2 (Table 1). With yields adjusted for days in milk and the previous 305-day lactation, the increase in milk production was significant for all three experiments, ranging from 6 to 11 percent greater than in the control groups.

 
Table 1

The researchers also projected milk yields for the rest of the lactation. The increases in supplemented cows compared to controls for an entire 305-day lactation ranged from 1,284 lbs (584 kg) per cow in Experiment 2 to 1,937 lbs (879 kg) per cow in Experiment 1. This extra production was worth $154 to $233 with milk priced at $12 per cwt (Figure 1). The supplemental beta-carotene cost $94.55 for the entire lactation, for a 64 to 147 percent return on investment.

 
Figure 1

Only cumulative milk yield was recorded for each cow, so the researchers could not report how soon the difference in milk yield appeared after supplementation began, or how quickly the difference grew. The researchers also did not project whether differences in milk production would increase if supplementation had continued through the entire lactation.

However, the researchers did find numerical differences in milk yields between cows with different lengths of beta-carotene supplementation. In Experiment 1, the cows that received beta-carotene for less than 90 days averaged 453 lbs (206 kg) more milk than controls at a comparable stage of lactation. This represented a 3.8 percent increase in milk yield with supplementation. The size of the increase tripled, to 11.4 percent, when the researchers compared milk yields from cows supplemented for 90 days or longer with the yields from their equivalent controls. Cows supplemented for at least 90 days produced 1,637 lbs (744 kg) more milk than cows at a comparable stage in lactation.

In Experiment 3, the researchers calculated milk production when supplementation occurred either for less than 60 days or for 60 days or more. The cows supplemented for less than 60 days produced 4.7 percent more milk than the equivalent control cows. When animals were supplemented for more than 60 days, the difference between supplemented and control cows rose to 8.7 percent.

This study was not designed to identify possible mechanisms for the increased milk production in supplemented cows, but the researchers noted that changes in body condition scores did not seem to be involved in the results. Heat stress also did not appear to be linked to the results, although the researchers first considered supplementation with beta-carotene because it has antioxidant properties and heat stress increases oxidative damage.

Indeed, while beta-carotene is perhaps best known as a vitamin A precursor, it has antioxidant properties that vitamin A itself does not have.

To date, much of the dairy research on beta-carotene, such as Chew (1994) has emphasized enhanced immune response--in particular, reducing the severity or incidence of mastitis. Several studies, such as those by Daniel et al. (1990) and Chew (1993), have also reported a role for beta-carotene in reducing somatic cell counts.

Physiologist Dr. Peter Hansen, who took part in the Florida research, suggests that higher milk yield may increase the antioxidant requirements in dairy cows. He further theorizes that the increased milk yield in supplemented cows could be due to increased antioxidant activity in the mammary gland and maintained function of alveolar epithelial cells.

Results of the study show that feeding supplemental beta-carotene to dairy cows at 400 mg per head daily for 60 to 90 days postpartum resulted in significant increases in milk yield. The return on investment was $59 to $137 per cow.

 

References:

  • Arechiga, C.F., et al., 1998. Effects of timed insemination and supplemental beta-carotene feeding on reproduction and milk yield of dairy cows under heat stress. J. Dairy Sci. 81:390.
  • Chew, B.P. 1993. Role of carotenoids in the immune response. J. Dairy Sci. 76:2804.
  • Chew, B.P. 1994. Beta-carotene, other carotenoids push immunity response. Feedstuffs. 66:18.
  • Daniel, L.R., et al., 1990. In vitro effects of beta-carotene and vitamin A on peripheral blood mononuclear cell proliferation. J. Dairy Sci. 74:911.

 
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