The “Pros” of Protein and the Merit of Methionine Supplementation in Late Pregnancy

Source: Ontario Ministry of Agriculture, Food and Rural Affairs

The last trimester is a crucial period for the cow to maintain body condition and body weight before lactation, while supporting rapid fetal growth and development. During this period over 60% of the growth of the calf and associated membranes occurs and nutrient requirements of the cow increase to support this growth (Bauman and Currie, 1980). Traditionally, a protein supplement may be provided to pregnant beef cows and has been shown to improve cow performance (Larson et al., 2014). On lower quality pastures, some producers may feed pregnant cattle an additional protein supplement at or above protein requirements in an attempt to improve dam health and future calf growth. However, this also adds energy to the diet, and it is not known if energy or protein has a greater impact on these factors. In addition, although protein supplementation can positively impact cow performance, it can also increase the nitrogenous waste excreted via feces and urine (Burgos et al., 2010). As the demand on producers to reduce their environmental impact increases, alternative options for oversupplying protein must be explored. One option is direct feeding single amino acids — which are the building blocks of protein, in order to provide a more complete protein to the animal. Methionine is most likely the first limiting amino acid in forage-fed beef cattle (Waterman et al., 2012). As a methyl-group donor methionine may also impact fetal programming responses, and influence future calf performance. Therefore, a recent trial was completed to assess the influence protein and methionine supplementation has on the performance of pregnant beef cows.

What we did

At the University of Guelph Elora Beef Research Center, ninety-nine cows and thirty-nine heifers were fed one of six diets formulated to either 90, 100, or 110% of total metabolizable protein (MP) requirements (NRC, 2016), with or without 9 g/d of rumen-protected methionine (Smartamine®M, Adisseo Inc.) for 60 days before their expected calving due date (Table 1). The cattle were individually fed in a calan gate system and offered a base TMR diet containing straw and haylage. Each individual animal was fed their respective supplement, such that their individual energy requirements for their weight and stage of pregnancy was equal between all protein treatments. Protein was balanced using soybean mean and energy was adjusted using palmitic fat. During the trial, cow performance was measured via body weight change. Pregnancy corrected body weight change was calculated to estimate weight of the cow without the fetus, associated membranes, and fluids (Silvey and Haydocks, 1978). Additionally, blood samples were taken prior to calving to monitor metabolic changes in the cow and total tract digestibility (TTD) was measured to estimate impact on diet digestibility.

Figure 2: Schematic of treatments allocation for cows and heifers fed for 60 d prior to expected calving due date.

Results

Cows fed at 90% MP requirements lost body weight (see Table 1), pregnancy corrected body weight (BW), and had reduced total tract digestibility. When cattle were fed above MP requirements they had higher dry matter (DM), crude protein (CP), acid detergent fiber (ADF) and energy (NEm Mcal/kg) digestibility. Supplemental MET did not affect cow performance; however blood results suggest rumen protected methionine supplementation increased glucose and reduced essential amino acids (EAA), branch chain AA (BCAA), and ketogenic AA serum concentrations (Table 2). Increasing dietary protein increased circulating urea concentrations (P <0.001) and reduced NEFA concentrations (P <0.03). This may suggest that although methionine had little impact on large-scale measurement like BW or body condition changes, there were differences in metabolic pathways, where methionine cows has increased glucose availability. If experimental treatments were more extreme this may have translated into performance differences. Neither protein or methionine supplement impacted calf birth. Thus, feeding cows below their MP requirements may limit late gestation performance and minimize forage digestibility.

Table 1. Performance and apparent total tract digestibility of cattle fed at 90, 100, and 100% metabolizable protein content in the diet

^z Different superscripts differ P>0.05. Methionine did not differ P > 0.10

Table 2. Serum amino acid and metabolite concentration in cattle fed with(without) rumen-protected methionine

^a,b,c Means within a dependent variable that have uncommon letters differ (P<0.05). Interaction between protein and methione did not differ (P > 0.1)
^zEssential AA = Arg, His, Ile, Leu, Lys, Met, Phe, Thr, Trp, and Val

^yNonessential AA = Ala, Asn, Asp, Cys, Gln, Glu, Gly, Pro, Ser, and Tyr

^xGlucogenic AA = Ala, Asn, Asp, Cys, Gln, Glu, Gly, His, Met, Pro, Ser, and Val

^wBranch chain AA = Ile, Leu and Val

^vKetogentic AA = Leu and Lys

Implications in the Beef Industry

This study suggests that feeding beef cows below their metabolizable (MP) requirements was detrimental to performance and digestibility. Weight loss due to MP restriction could negatively impact the cow’s ability to lactate and rebreed successfully. Additionally, a reduction in digestibility may limit digestion and absorption of nutrients. Therefore, during late gestation producers should ensure their cattle are supplied adequate metabolizable protein, even when energy requirements are met.

Although methionine supplementation did not impact cow performance or digestibility parameters measured in the study, serum markers indicate that methionine is causing a change in glucose and AA metabolism in late gestation. However, this study yielded no evidence that methionine can replace additional protein in the diet to improve cow performance or apparent total tract digestibility during late gestation. Current work is underway evaluating the impacts of these treatments on offspring performance as a result of late gestation protein and methionine supplementation.

Author: Madeline Collins and Dr. Katie Wood – University of Guelph