Relationship between performance, metabolic profile, and feed efficiency of lactating beef cows.

Twenty-seven Nellore cow-calf pairs were submitted for feed efficiency testing. The animals were weighed every 21 ± 5 days to obtain metabolic body weight (BW0.75) and average daily gain (ADG). Subcutaneous fat thickness (SFT; at 20, 83, 146, and 176 days post-calving); milk yield and components (63, 85, and 151 days); levels of glucose, cholesterol, triglycerides, ß-hydroxybutyrate, albumin, urea, creatinine, calcium, phosphorus, magnesium, insulin, and cortisol (15, 41, 62, and 124 days); and ingestive behavior were evaluated. Residual feed intake was calculated for the first stage (RFI1; 21 to 100 days post-calving) and the second stage of lactation (RFI2; 100 to 188 days post-calving), and the cows were classified based on RFI1 as most efficient (RFI1 < 0) and least efficient (RFI1 > 0). Negative RFI1 cows consumed 1.3 kg/day of dry matter, or 9.77%, less than positive RFI1 cows. Most- and least-efficient cows did not differ in terms of subcutaneous fat thickness traits and milk yield or energy-corrected milk (ECM). Glucose (P = 0.0785), triglycerides (P = 0.0795), and phosphorus (P = 0.0597) concentrations were higher in the first stage of lactation in most-efficient cows. Maternal characteristics such as calf weight at birth and at 205 days and ADG were similar in most- and least-efficient cows. The most-efficient cows are more economic as they consume less feed for the same level of production.

Energy balance in grazing Jersey cows in early lactation supplemented with peanut and sunflower oils.

In this study, we evaluated the effects of supplementation with peanut and sunflower oils on intake and digestibility, milk yield and composition, energy balance (EB), changes in weight and body condition score (BW and BCS), and blood metabolites of Jersey cows on pasture in early lactation. Twenty-four cows were distributed in a randomized block design where they received the following treatments: concentrate without oil (CON), concentrate plus 59.6 g/kg DM peanut oil (PEA), concentrate plus 59.6 g/kg DM sunflower oil (SUN), and concentrate plus 59.6 g/kg DM of a 1:1 mixture of peanut oil and sunflower oil (MIX). The data were analyzed at 30 and 60 days in milk (DIM). Oil supplementation did not affect total dry matter intake or forage intake. The treatment SUN reduced daily milk yield, 4% fat-corrected milk yield, and milk fat, while the other treatments generated similar results. The treatment SUN reduced the milk net energy and the use efficiency of the NEL for milk production and BW and BCS changes, and improved EB up to 60 DIM. On tropical pastures, supplementation with unsaturated oils for cows in early lactation does not result in better milk performance. The supplementation with sunflower oil improves the energy balance in early lactation.