Yeast of Saccharomyces cerevisiae (SCY) origin has over long time been incorporated into domestic animal diets. In calves, several products have offered improved performance and health. Although several types of research have been completed, the mode of action of SCY is not clear in calves. Under this review, we have highlighted the works available in the literature on the use of SCY in calves performance, health, immunity, and the gut environment. Both active live yeast and yeast culture have positive effects on growth, rumen, small intestines, immunity and general health of the calf. Specifically, SCY can improve DMI, growth, feed efficiency and reduce diarrhea in calves. Furthermore, subtle improvements are seen in rumen fermentation (increased butyrate production) and rumen papillae growth. These positive results are, however, more pronounced in calves that are under stress or exposed to significant levels of disease-causing agents. There is a need for further research in areas such as gut morphology, gut microbiology and immunity using latest molecular methods to fully understand how SCY helps the growth and development of calves.

The present experiment was performed to assess the effects of different sources of milk on the growth performance, serum metabolism, immunity, and intestinal development of calves. Eighty-four Holstein male neonatal calves were assigned to one of the following four treatment groups: those that received bunk tank milk (BTM), untreated waste milk (UWM), pasteurized waste milk (PWM), and acidified waste milk (AWM) for 21 d. Calves in the BTM and AWM groups consumed more starter (P < 0.05) than those in the UWM group. Average daily gain in the UWM group was the highest (P < 0.05). Calves exhibited the highest (P < 0.05) serum total protein, albumin, total cholesterol, high density lipoprotein, triglycerides, growth hormone, immunoglobulin (Ig) A and IgM concentrations in the UWM group, highest malondialdehyde and tumor necrosis factor-α in the PWM group (P < 0.05), and highest glutathione peroxidase and IgG in the BTM group (P < 0.05). The jejunum and ileum of the calves in all treatments presented a slight inflammatory response. The jejunal inflammation scores were higher (P < 0.05) in the UWM and AWM groups than the BTM group; the ileal inflammation scores increased more (P < 0.05) in the AWM group than the BTM group. Jejunal immunohistochemical scores (IHS) were higher (P < 0.05) in the PWM and AWM groups than the BTM group. Compared to the other three groups, calves feeding on BTM had lower (P < 0.05) ileal IHS. Jejunal interleukin(IL)-1β, IL-8, and IL-10 mRNA expression in the UWM group was the highest (P < 0.05). Calves fed AWM increased (P < 0.05) mRNA expression of IL-8 and toll like receptor 4 (TLR-4) in the jejunum and IL-8, IL-1β, IL-6, IL-8, and IL-10 in the mesenteric lymph nodes. Overall, bunk tank milk is the best choice for calf raising compared to waste milk. The efficiency of feeding pasteurized and acidified waste milk are comparable, and the acidification of waste milk is an acceptable labor-saving and diarrhea-preventing feed for young calves.

High-altitude pulmonary hypertension (HAPH) is a life-threating condition for animals in high altitude, and disturbance of endothelial nitric oxide (NO) synthesis contributes to its pathogenesis. N-carbamylglutamate (NCG), which enhances arginine synthesis, promotes endogenous synthesis of NO. In this study, we determined the effects of NCG on alleviating HAPH in Holstein heifers that ascended to Tibet (Lhasa, 3,658 m). Exp. 1, 2,000 Holstein heifers were transported from low elevation (1,027 m) to Lhasa. After being exposed to hypoxia for 1 yr, Holstein heifers were assigned to a healthy group (Control, n = 6) with mean pulmonary hypertension (mPAP) < 41 mmHg, and an HAPH affected group (HAPH, n = 6) with mPAP > 49 mmHg. Lung tissues were collected to evaluate histopathological changes and the expression of endothelial nitric oxide synthase (eNOS). Exp. 2, ten healthy heifers and 10 HAPH affected heifers were supplemented with NCG (20 g/d per heifer) for 4 wk. Physiological parameters were determined and blood samples were collected on d − 1 and d 28 of the feeding trial. Expression of eNOS in small pulmonary arteriole intima was higher in the healthy than HAPH group (P = 0.006), whereas HAPH group had significantly thicker media and adventitia than healthy group (all P < 0.05). The mRNA of eNOS and protein level of eNOS were higher in the lungs of heifers in the healthy group than in the HAPH group (both P < 0.001), whereas endothelin-1 protein levels were higher in HAPH group than in the healthy group (P = 0.025). NCG supplementation decreased mPAP and ammonia (both P = 0.001), whereas it increased the expression of eNOS, arginine, and plasma NO (all P < 0.05). The expression of eNOS was decreased in Holstein heifers with HAPH. NCG supplementation decreased mPAP through the restoration of eNOS and endogenous NO synthesis.