Fatty acid profiles, growth, and immune responses of neonatal lambs fed milk replacer and supplemented with fish oil or safflower oil

Diets supplemented with long chain, n−3 polyunsaturated fatty acids (PUFA) have improved the health and performance of neonatal and growing animals. This study was conducted with lambs that were orphaned at approximately 1 day of age to determine whether supplementing milk replacer fed lambs with oils rich in long chain n−3 or n−6 PUFA would alter plasma lipid profiles and affect growth characteristics and immune functions. From days 1 to 28 of age, lambs had ad libitum access to commercial milk replacer. From days 7 to 28 of age, lambs received twice daily either 1 g of soybean oil, 1 g of fish oil, or 1 g of safflower oil per os in a gelatin capsule (n = 60 pens; 20 pens/treatment; one ewe and one ram with similar initial body weights/pen). On days 7, 14, 21, and 28 of age, lambs were weighed, and jugular blood was collected from ram lambs. Lymphocyte proliferation in vitro, differential white blood cell (WBC) counts, and weight gains were quantified. Plasma from days 7 and 28 was used for fatty acid analyses. Fish oil increased (P < 0.001) plasma total n−3 fatty acid concentration and total n−3:total n−6 fatty acid ratio. Pen body weight (i.e., total lamb weight per pen) increased (P < 0.001) with day (day 7, 11.9 kg; day 14, 15.1 kg; day 21, 18.2 kg; and day 28, 21.2 kg), but oil treatment did not affect pen body weight. Neither oil treatment, day, nor oil treatment×day interaction were significant for pen body weight gains (3.5 kg), pen average daily gains (0.5 kg), pen milk intakes (19.0 kg), or pen gain:feed ratio (0.18) measured during three intervals: days 7–14; days 14–21; and days 21–28. Day, but not oil treatment, affected (P < 0.001) unstimulated, concanavalin A stimulated, and lipopolysaccharides stimulated lymphocyte proliferation: days 14, 21, and 28 proliferation > day 7 proliferation. For neutrophils per 100 WBC, the treatment×day interaction was significant (P < 0.05). Oil treatment and day affected (P < 0.01 and <0.05, respectively) lymphocyte numbers per 100 WBC. For monocytes, eosinophils, and basophils, neither oil treatment, day, nor the oil treatment×day interaction were significant. Fish oil altered plasma fatty acid profiles, but it did not seem to improve measures of the performance or immune function of healthy, milk replacer fed lambs.