Pre- and postpartum effects of starch and fat in dairy cows: A review
This review discusses the effects of starch and fat before and after calving on metabolism, energy balance (EB), milk production, and reproduction in dairy cows. The shift in dairy cows from a pregnant non-lactating state to a non-pregnant lactating state induces physiological changes, which affect the metabolic and endocrinal axes to redirect body energy stores towards the mammary gland for milk production. Overfeeding high starch and fat levels during the dry period after calving may result in cows failing to adapt to the negative energy balance (NEB) because of major liver and rumen dysfunction. Alternatively, keeping dry cows on high-forage/low-energy diets adjusts dry matter intake (DMI) to optimize the rumen function and decrease the severity of the NEB during transition. These periparturient biological improvements in dairy cows showed real benefits such as fewer postpartum health complications (e.g. milk fever, ketosis, mastitis, metritis), decreased body condition loss and improved reproductive axis in the subsequent lactation. Adding dietary starch and/or fat to diets of dairy cows following parturition increased milk yield. In addition, milk protein of dairy cows increased with glucogenic diets, but decreased with lipogenic diets. Inversely, milk fat usually increases after feeding lipogenic diets, but it decreases when feeding glucogenic diets to dairy cows. Glucogenic and lipogenic nutrients can affect the cow’s metabolism and its EB status positively, as is evidenced by plasma non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB), glucose, amino acids, insulin, insulin-like growth factor-I (IGF-I), growth hormone (GH), gonadotropin hormones, and progesterone (P4) levels. These metabolites (NEFA, BHB, glucose, amino acids) and hormones (insulin, IGF-I, GH, P4) have been shown to affect folliculogenesis, ovulation, conception, and pregnancy success. Feeding a starch-based diet to dairy cows can lead to acidosis and increase glucose and insulin levels, while decreasing NEFA and BHB levels. Furthermore, an insulinogenic diet favours an early resumption of ovarian activity, but has adverse effects on the quality of oocytes. In contrast, keeping dairy cows on a fat-based diet elevates NEFA and BHB levels and decreases glucose and insulin levels. Additionally, a lipogenic diet increases the plasma P4 levels and improves the quality of oocytes. These evidences suggest that reproductive performances in dairy cows can be enhanced by feeding an insulinogenic diet until the resumption of the ovarian cycle then switching to a lipogenic diet from mating period onwards. Since long-term field studies on fertility are limited and the reproduction process in dairy cows is multi-factorial, further research is needed on the pre- and postpartum effects of starch and/or fat as well as their combinations on reproduction axis and thus to draw conclusions on reproductive performances.
Keywords: Digestion, energy nutrients, metabolism, milk production, reproduction, ruminant