The transition period for small ruminants: balanced nutrition is frequently understate but makes the difference

The transition period is extremely delicate for all ruminants, including sheep and goats. In these species, the transition starts 2-3 weeks before and lasts 2-3 weeks after calving. During this period the animal physiology drastically changes:

• There are higher nutrients requirements for the last part of the pregnancy by one or more fetuses;
• The lambing is a stressful event for sure;
• There is a reduction in feed intake and an appetite fluctuation;
• The mammary gland prepares itself for lactation ;
• There is a dietary change;
• There is a general hormonal change.

The result is a huge increase in energy requirement with a reduced energy availability: as well as for dairy cows, sheep and goats experience a negative energy balance (NEBAL) worsen by the fact that multiple births are very frequent in these species. The body mobilizes the endogenous lipid sources to produce more energy but the hepatic metabolism is unable to meet the high requirements of the transition period. The liver transforms the non-esterified fatty acids (NEFA) into triglycerides. These molecules must be transferred to the bloodstream through the very low-density proteins (VLDL), but the hepatic synthesis of these proteins is not sufficient. Moreover, the high amount of NEFA in the liver leads to the production of ketone bodies such as BHBA (Zang et al., 2019). Thus, there is a high risk of clinical or sub-clinical signs of “pregnancy toxemia” (Wand, 2010).

The animal management during this period must take into account their physiological and metabolic condition. To reduce the NEBAL can be useful to separate animals with twin pregnancy from the others. In this way it is easier to balance the diet based on the real animal requirements, avoiding a strong energy deficiency for animals with higher genetic merit and preventing an excessive weight increase for the animal with only one fetus.

Rumen-protected amino acids are useful tools during the transition period. Rumen-protection allows the maximization of the dietary supplementation, avoiding rumen degradation with an accurate balance of the diet. In addition to improving milk production, several studies show that amino-acids (and their correct balance, especially for the limiting ones) are involved in the hepatic metabolism of fatty acids and the transport of long-chain fatty acids from the bloodstream to the udder (Glascock and Welch, 1974; Madsen et al., 2005; Tsiplakou et al., 2017). The most known and used is methionine. Moreover, methionine and vitamins of the B group (B₁₂ in particular) are involved in glutathione production. Glutathione-transferase is a fundamental enzyme for reactive oxygen species (ROS) and other oxidant molecules reduction. Thus, the contemporary administration of methionine and vitamin B₁₂ has a positive effect on the animal’s ability to face oxidative stress (Halsted, 2013). Even if methionine is the most studied molecule for ruminant nutrition, there are two most important methyl donors for these species. The first one is a methionine metabolite, the S-adenosyl-L-methionine (SAM), while the second is betaine, a choline metabolite.

Choline is directly involved in the hepatic lipid metabolism and is as important as methionine in ruminants. This molecule is part of the glycerophospholipids metabolism: it is part of the phosphatidylethanolamine (PE) methylation and phosphatidylcholine (PC) synthesis (Figure 1). A deficiency of these two molecules, especially of PC, is strictly correlated to fatty liver in transition animals. Choline dietary supplementation is commonly recognized as a useful tool to prevent hepatic steatosis (McFadden, 2018; Cooke et al., 2007).

Figure 1: The complex synthesis and degradation of phosphatidylcholine.
CDP = cytidine diphosphate; CMP = cytidine monophosphate; CPT = choline phosphotransferase; DAG = diacylglycerol; HCY = homocysteine; LPCAT = LPC acyltransferase; PEMT = phosphatidylethanolamine N-methyltransferase; PLA2 = phospholipase A2; SAH = S-adenosylhomocysteine; SAM = S-adenosylmethionine. (Form: McFadden, 2018).

The second most important methyl donor is obtained from choline, betaine. This molecule is a byproduct of sugar beet processing and can be extracted by chromatographic separation and subsequent crystallization from molasses. In tissues, betaine is an osmolyte maintaining cell trophism and enters the hepatic lipid metabolism (Peterson et al., 2012). It was demonstrated that betaine dietary supplementation in lactating small ruminants leads to improved milk production and higher concentration in milk fat and protein (Fernandez et al., 2004 and 2009). Betaine is extremely important in several metabolic processes and is produced by the organism starting from choline. To prevent the use of part of the ingested choline as a betaine source it is useful to supplement the diet with both these molecules during the transition period.

Rumen microflora uses and/or degrades the vast majority of the cited nutrients. The rumen bypass is of pivotal importance to give the right nutrient concentration to the animal. Tsiplakou et al. (2017) demonstrated that the supplementation of methionine, choline, betaine, and vitamin of the B group at the same time helps to sustain the animal for a longer period both before and especially after starting lactation to prevent hepatic steatosis and related pathologies. In this specific study, a combination of methyl donors and vitamins in a rumen-protected (microencapsulated) form was added to Chios ewes diet during the transition period (from 15 days before to 60 days after lambing). This treatment was compared to a standard diet and another diet only supplemented with protected methionine. Results (Table 1) showed that the feed additives combination is more effective in improving milk production. Moreover, treated animals had better antioxidant systemic activity (the “ferric reducing ability of plasma”, FRAP) and lower plasma β-BHB concentration.

Table 1: Milk production and plasma parameters of sheep receiving standard diet (alfalfa hay, wheat straw, concentrates) with or without rumen-protected methionine or rumen-protected combination of methyl donors and vitamins B (methionine, choline, betaine, vitamin B_2, and B₁₂)

In conclusion, the transition period is particularly stressful for sheep and goats, that frequently have clinical signs of hepatic steatosis. Good herd management helps to maintain animals’ health during this specific period. The first thing to do is to determine the real requirements of the animals based on their kind of pregnancy (twins or single fetus). In this way, we can balance their dietary energy intake in the best way possible. Another useful tool is to supplement all the transition diet with methyl donors and vitamins of the B group to sustain hepatic lipid metabolism, production, and milk quality up to lactation peak.For more information: marketing@vetagro.comOriginal article here.