The most critical weeks in a lamb's life are its first few on the ground. In a 1988 survey by Montana State University, for instance, 12 percent of all lambs born didn't survive even until docking; these early deaths accounted for about two--thirds of the lambs that did not survive to a marketable age. Besides cold stress and starvation, a primary cause of early mortality was pneumonia, emphasizing the importance of passive immunity to infectious agents through adequate transfer of maternal antibodies in the colostrum.
Because research has suggested enhanced humoral immunity in vitamin E supplemented livestock, scientists are also studying the possible effects of vitamin E supplementation on passive immunity and early lamb survivability. Recent work (Thomas et al., 1995) at Montana State University found that when ewes were fed dietary supplemental vitamin E, lamb mortality rates were as much as 50 percent lower compared to control ewes. In the study, supplemented ewes received 330 IU of vitamin E daily from approximately three weeks before lambing until giving birth.
All told, supplemented ewes weaned about eight percent more lambs--121.9 lambs per 100 ewes, versus 112.7 for the control ewes. The difference in survivability was even more pronounced among ewes that gave birth early in the season (on or before April 15), when environmental stress from bad weather was greater. Lamb mortality rate during the early season was 8.6 percent for supplemented ewes and 15.5 percent for unsupplemented ewes. Because of this increased livability, total lamb production was 5 lbs (2.3 kg) greater per ewe in the vitamin E supplemented group. Unpublished data from the second year of the study show a similar decline of about 50 percent in lamb mortality with supplemented ewes.
These results are in keeping with those from other studies, such as Kott et al. (1983), in which ewes received monthly injections of 272 IU of vitamin E. In that study, percentage of lambs weaned totaled 95.0 for supplemented ewes and 87.4 for the control group. Lamb deaths were primarily due to weakness at birth, failure to nurse and pneumonia. Because of the difference in early mortality rate, lambs weaned per bred ewe averaged 1.6 for the supplemented group and 1.4 for the unsupplemented ewes.
The reasons for higher survivability with vitamin E supplementation are less clear than the results. Gentry et al. (1992) measured serum vitamin E and immunoglobulin G (IgG) levels after injecting ewes with 1,500 IU of vitamin E at 21 days before lambing and again at lambing. The researchers found increased serum vitamin E levels in both ewes and lambs with supplementation.
IgG levels were more complicated, however. When the researchers measured IgG levels in the colostrum itself, they found no difference between supplemented and unsupplemented ewes, although lambs from supplemented ewes had increased IgG levels starting the first day after birth. In addition, when lambs from unsupplemented ewes were given 900 IU of vitamin E by injection at birth, they also had increased serum IgG levels compared to the controls, though the increase did not appear until three days after injection. Gentry et al. say these results suggest that vitamin E may enhance absorption of colostral antibodies in lambs. They note that similar results, describing increased IgG transfer with vitamin E supplementation, have been reported in pigs (Hayek et al., 1987).
However, in a second study by the Montana researchers (Bohn et al., 1995), there was no difference in IgG levels for either lambs or ewes by treatment group. Vitamin E levels in the ewes' colostrum and the lambs' serum did increase with ewe supplementation.
Although measurement of immunoglobulin quantity is widely accepted, a procedure to assess immunoglobulin quality has not yet been established. Differences in immunoglobulin quality could partially explain the responses of vitamin E supplemented ewes.
Whatever the mode of action with vitamin E supplementation, Dr. Verl Thomas at Montana State notes that getting lambs over the early mortality hump is even more important with the current ability to increase the percentage of twin or triplet births. While these births offer the potential for more lambs produced per exposed ewe, it is also true that lambs from multiple births are even more susceptible to disease and death than single lambs.
References:
- Bohn Jr., G.P., et al., 1995. Effects of prepartum supplemental dl-a-tocopherol acetate on placental and mammary vitamin E transfer and lamb immunoglobulin concentrations. Proc. West. Sec. Am. Soc. Anim. Sci. 46:24.
- Gentry, P.C., et al., 1992. Effects of supplemental d-a-tocopherol on preweaning lamb performance, serum and colostrum tocopherol levels and immunoglobulin G titers. Sheep Research J. 8:95.
- Hayek, M.G., et al., 1987. Immunoglobulin transfer to pigs from sows injected with vitamin E and/or selenium. Prog. Rep. Kentucky Agri. Exp. Sta. 299:31.
- Kott, R.W., et al., 1983. Effects of vitamin E and selenium injections on reproduction and preweaning lamb survival in ewes consuming diets marginally deficient in selenium. J. Anim. Sci. 57:553.
- Thomas, V.M., et al., 1995. The influence of late pregnancy feeding of vitamin E on lamb mortality and ewe productivity. Proc. West. Sec. Am. Soc. Anim. Sci. 46:91.
