Effects of dietary electrolytes, osmolytes, and energetic compounds on body temperature indices in heat-stressed lactating cows

Objectives were to determine the effects of a product containing electrolytes, osmolytes, and energetic compounds (EOEC) on body temperature indices in heat-stressed (HS) Holstein cows. Lactating cows were assigned to 1 of 2 treatments: 1) a control diet (n = 10) or 2) a control diet supplemented with 113 g/d of EOEC (n = 10; Bovine BlueLite® Pellets; TechMix LLC, Stewart, MN). The trial consisted of 2 experimental periods (P). During P1 (4 d), cows were fed their respective treatments and housed in thermoneutral conditions. During P2 (4 d), HS was artificially induced using an electric heat blanket (EHB). Overall, HS markedly increased vaginal temperature (Tv), rectal temperature (Tr), skin temperature (Ts), and respiration rate (RR) (P < .01). There were no dietary treatment differences in Tv, Tr, or RR; however, during P2 EOEC-supplemented cows had increased Ts (0.8 °C; P = .04). Compared to P1, HS decreased DMI and milk yield (45 and 27%, respectively, P < .01) similarly amongst treatments. Relative to P1, circulating insulin decreased (41%; P = .04) in CON cows, whereas it remained unaffected in EOEC-supplemented cows, resulting in a 2-fold increase in EOEC compared with CON-fed cows (P < .01) during P2. Relative to P1, HS increased circulating non-esterified fatty acids (NEFA; 63%; P < .01). During P2, there tended to be a treatment by day interaction on circulating NEFA, as concentrations decreased from d 2 to 4 of P2 in EOEC-fed cows but continued to increase in CON cows. In summary, feeding EOEC altered some key aspects of energetic metabolism and increased Ts.

Simulation of cow-calf production systems in a range environment: I. Model development

A mathematical computer model of beef cattle production systems was developed at Montana State University. The objective of this report was to describe the rationale and procedures used to simulate animal and system performance. The model was designed to simulate the dynamic relationships among cattle genotype, physiological state, forage quality, and management in range environments. Forage intake, energy and protein metabolism, growth, reproduction, lactation, and changes in chemical body composition are simulated for individual animals over complete life cycles. Expenses driven by animal performance, management decisions, and land resources are tabulated. Several biological and economic measures of system performance can be computed, including ratios of inputs (e.g., DM, CP, ME, dollars) to outputs (e.g., weight, lean), break even prices, and annual gross margin per cow or ranch. Primary uses of the model include the evaluation of system responses to changes in breeding strategies and management in range production/marketing systems.

Simulation of cow-calf production systems in a range environment: II. Model evaluation

Development of a general beef cattle simulation model was described in a companion paper. The objectives of this research were to demonstrate and evaluate the model's performance. Four experiments were conducted to demonstrate 1) life-cycle weight and body condition changes for different genotypes raised in a northern range environment; 2) responses in forage intake and weight to changes in forage quality, protein supplementation, and cow physiological state; 3) responses in reproduction, weight, body condition, and calf growth to differences in pre- and postpartum nutrition; and 4) differences in enterprise efficiency and profit for different genotypes and mating systems. Results indicated that the model performs acceptably for the types of situations for which it was designed and highlighted areas of animal science where more information is needed in order to better understand and manipulate beef cattle systems. Computer simulation models are useful tools to facilitate the integration of scientific concepts and to help scientists, teachers, and producers better understand the complex production systems that they study and manage. In addition to addressing enterprise-level problems that are beyond the scope of traditional experimentation, modeling and simulation help identify research needs and foster exchange among disciplines.

Development of an udder health index for sire selection based on somatic cell score, udder conformation, and milking speed

Genetic parameters of subjectively scored milking speed and somatic cell score were estimated using REML and a sire model. Approximately 250,000 records were used. Heritabilities were 0.15 for milking speed and 0.14 and 0.16 for lactation mean somatic cell score (SCS) for first and second lactations, respectively. Genetic correlations between milking speed and SCS were 0.41 and 0.25 for first and second lactations, respectively, indicating that faster milking was associated with increased SCS. Genetic parameters for milking speed, SCS, and udder conformation were estimated using REML and an animal model. Records from approximately 120,000 cows were used. Genetic correlations were greatest for udder depth (-0.26) with SCS and for width of rear udder attachment (-0.24) with milking speed. An udder health index for use in sire selection was developed for an aggregate genotype that included subclinical mastitis in lactations 1 and > or = 2, clinical mastitis in lactations 1 and > or = 2, and milking time. Respective economic weights were -$12, -$31, -$15, -$59, and -$11 per genetic standard deviation. Traits in the selection index were milking speed, udder conformation, and SCS in first and later lactations. Standardized weights for a simple index for sires based on estimated breeding value from 50 daughter records were 5.5, -1.2, 3.5, -3.9, and -8.7 for udder depth, front teat length, milking speed, and SCS for first and later lactations, respectively. The accuracy of the index was 0.776, an increase of 15% over an index with only SCS.