Merlyn K. Nielsen

Extended grazing systems for improving economic returns from Nebraska sandhills cow/calf operations

Three winter treatments were cross classified with 2 spring treatments to create 6 feeding and grazing systems utilizing Nebraska sandhills range and subirrigated meadow forage. Systems were evaluated with multiparous crossbred beef cows over 4 years (240 head beginning year 1). Systems were: 1) owing range during winter; 2) grazing subirrigated meadow during winter; and 3) fur feed of meadow bay during winter; in combination with either: a) full feed of subirrigated meadow hay during May, or b) grazing subirrigated meadow during May. From June through November all cows grazed range. The feeding and grazing systems were compared with selected linear contrasts and evaluated with respect to variable input prices. Some differences in cow body weight and body condition occurred but differences were considered small. Throughout the study, cows on all systems generally maintained a body condition score of about 5 (1 to 9 scale) year long. Inputs of hay were reduced by grazing range or subirrigated meadow during winter and during May without affecting pregnancy rate. Weaning weight of calves was increased 5.0 kg by grazing meadow during May compared to feeding hay during May. When opportunity costs were included in the analysis, the most profitable system involved grazing subirrigated meadow during winter and during May. Grazing subirrigated meadow during May enhanced the profitability of all wintering systems.

Variability in metabolic rate, feed intake and fatness among selection and inbred lines of mice

Mouse populations differing in metabolic rate have been developed through selection for high (MH) and low (ML) heat loss (HLOSS), along with randomly selected controls (MC). Objectives of this study were to (a) compare MH, ML and MC lines for HLOSS and correlated traits of feed intake, body composition and organ weights; (b) compare three widely used inbred mouse lines with MH, ML and MC for the same traits; and (c) investigate potential genotype by diet interaction resulting from feeding diets differing in fat percentage. Heat loss (kcal/day) of MH and ML mice differed by 37% of the mean and remained significant (33%) when HLOSS was expressed on a fat-free mass basis. MH mice consumed more energy than ML with a greater difference in mice fed high-fat compared with standard diets (27% vs 13.9%). Despite greater energy consumption, MH mice were leaner than ML with a difference in total body fat percentage of 40%. The greatest difference in HLOSS between selection and inbred lines was between MH and C57BL/6J (BL), which differed by 26.3%. MH and BL mice also differed in energy intake (15.5%). Body composition of BL mice was similar to MH when fed a standard diet, but similar to ML when fed a high-fat diet. Crosses between MH and ML or between MH and BL would be useful to investigate the genetic regulation of, and identify quantitative trait loci influencing HLOSS, energy intake and body composition. Feeding of a high-fat diet may allow diet-specific loci influencing body composition to be identified in MH and BL lines.

Markov chains as a shortcut method to estimate age distributions in herds of beef cattle under different culling strategies.

Markov chains were used to estimate the age distribution at equilibrium and average age in herds of beef cattle and the age distribution and average age of culled cows. These estimates are essential in systems simulation and economic analyses of beef production alternatives because the biological input and output from a beef production system depend on the age structure of the cows in the system. Ten sets of data on age-specific probabilities of culling for different reasons were found in the literature and used in simulation of different culling strategies. Three different culling strategies were simulated using these data. In addition to culling on maximum age, culling was either based on health alone, health and reproductive failure in one year (not pregnant) or health and reproductive failure in two consecutive years (not pregnant twice). The average herd age in the data sets reviewed under the actual culling strategies ranged from 4.58 to 6.73 yr and the average age of culled cows ranged from 5.41 to 9.94 yr. Description of the culling process as a Markov chain enables calculations of the age distribution at equilibrium by simple matrix operations, an advantage over the methods presently used. The scarcity of estimated age-specific probabilities of health and reproductive failure points to the need for more population analyses of beef cattle.

A polymorphic glucocorticoid receptor in a mouse population may explain inherited altered stress response and increased anxiety-type behaviors

A polymorphic glucocorticoid receptor (GRQn) with an expanded CAG track and two silent mutations, when compared with the sequence of other isoform (GRwt), is found in two outbred mouse lines that were produced by selection for high (SH) or low (SL) stress response from high or low heat loss lines of mice, respectively. The GRQn allele, which is also found in 5 of 16 commonly used inbred mouse lines, had a much higher frequency in SL mice; the GRwt/wt was found only in the SH line. Both GRQn/Qn and GRwt/Qn mice had a much weaker corticosterone response to stress than the GRwt/wt mice. Assessment of open field activity revealed that GRQn/Qn and GRwt/Qn mice exhibited significantly lower velocity and locomotor activity, less time in the center, and much longer duration in corner zones than the GRwt/wt mice. The increased anxiety‐type behaviors of the GRQn/Qn and GRwt/Qn mice were confirmed by the “elevated plus maze” test in which GRQn/Qn and GRwt/Qn mice spent significantly less time in the “open arm” and longer duration in the “closed arm,” than GRwt/wt mice. These results suggest this GR polymorphism plays a role in complex mechanisms leading to lower corticosterone response to stress, and may also be associated with decreased locomotive and increased anxiety‐type behaviors in mice.—Xu, D., Buehner, A., Xu, J., Lambert, T., Nekl, C., Nielsen, M. K., Zhou, Y. A polymorphic glucocorticoid receptor in a mouse population may explain inherited altered stress response and increased anxiety‐type behaviors. FASEB J. 20, E1802–E1810 (2006)

Selection for maternal behavior in mice—direct and correlated responses

Abstract Three generations of divergent selection for a maternal care index (MCI) in mice were practiced in each of three replicates. MCI was recorded for 29–32 dams and litters in each replicate/line subclass. Pups of the top (or bottom) 6–10 dams in each replicate, depending on number of females in the litters, were selected in high (H) and low (L) MCI lines. At birth, litters with more than 10 pups were standardized to 10 pups whereas litters with no more than 10 pups remained intact. On day 4, 8, 12, and 16 of lactation, time budgets during a 30-min session were recorded by real-time video camera. The times spent in the activities of nursing pups, licking pups, retrieving pups, resting with pups, and building a nest were summed, and MCI was the percentage of the total time devoted to these activities. Number born alive (NBA), number weaned (NW), litter weaning weight (LWW), and mating weight (MW) were recorded. The difference between H and L in cumulative selection differential (CSD) of MCI was 59.8%. Regressions of differences in H and L on generation and on cumulative selection differential were 4.878±0.414 and 0.239±0.011 (realized heritability), respectively ( P P

Genetic variance and covariance patterns for body weight and energy balance characters in an advanced intercross population of mice

We estimated heritabilities and genetic correlations for a suite of 15 characters in five functional groups in an advanced intercross population of over 2000 mice derived from a cross of inbred lines selected for high and low heat loss. Heritabilities averaged 0.56 for three body weights, 0.23 for two energy balance characters, 0.48 for three bone characters, 0.35 for four measures of adiposity, and 0.27 for three organ weights, all of which were generally consistent in magnitude with estimates derived in previous studies. Genetic correlations varied from -0.65 to +0.98, and were higher within these functional groups than between groups. These correlations generally conformed to a priori expectations, being positive in sign for energy expenditure and consumption (+0.24) and negative in sign for energy expenditure and adiposity (-0.17). The genetic correlations of adiposity with body weight at 3, 6, and 12 weeks of age (-0.29, -0.22, -0.26) all were negative in sign but not statistically significant. The independence of body weight and adiposity suggests that this advanced intercross population is ideal for a comprehensive discovery of genes controlling regulation of mammalian adiposity that are distinct from those for body weight.

Heifers sired by bulls with either high or low expected progeny differences (EPDs) for marbling do not differ in age at puberty

Abstract Selection for carcass traits such as deposition of intramuscular fat (marbling), which is a primary trait used as an indicator of meat quality, may incur additional effects such as younger age at puberty. Therefore, a trial was conducted for 2 years to determine age of puberty for two groups of crossbred heifers ( n = 124) sired by purebred Angus bulls selected for either low (Low, n = 6) or high (High, n = 6) expected progeny differences (EPDs) for marbling. Our working hypothesis was that age at puberty would be reduced in heifers sired by bulls with high EPDs for marbling in comparison to those heifers sired by bulls with low EPDs for marbling. Puberty was determined by collecting weekly blood samples and assaying for concentrations of progesterone. Mean age at puberty for heifers during the study did not differ (392 ± 5 and 387 ± 5 days, Low and High respectively). Of the 124 heifers, 79% reached puberty within the 145 days allotted for the study. We conclude that use of sires that produce daughters with increased ability to marble does not result in decreased age at puberty.

Maternal behavior in mice selected for large litter size

Abstract A total of 96 lactating mice and their pups from each of three replications of lines selected 21 generations for increased litter size (LS) followed by 23–25 generations of random selection and contemporary unselected control lines (LC) were characterized for maternal behavior. Sixteen dams and their pups from each replication of LS and LC lines were sampled. Litter sizes at birth for LS versus LC in the first, second, and third replicates were 17.3 versus 13.2, 15.9 versus 13.1, and 12.3 versus 10.6 pups, respectively, with LS dams averaging 2.87±.70 pups more. One-half of the litters were standardized to either 12 pups (Replications 1 and 2) or 8 pups (Replication 3) on day 1 of lactation; the others were not standardized. Behavioral categories included time dams spent: (1) nursing pups, (2) licking pups, (3) retrieving pups, (4) nest building, (5) resting with pups, (6) resting alone, (7) eating and drinking, (8) grooming, and (9) in other activities. Categories one through five were summed as an index of maternal behavior. Activities during 30min observation periods from days 2 to 22 of lactation were recorded. Interactions of line by stage of lactation (days 2–4, 5–8, 9–12, 13–17, and 18–22) and line by litter standardization were not significant for any trait except time spent resting with pups (line × stage, P =0.03). The maternal behavior index was 7.0±2.2% greater ( P =0.08) for LS than LC dams. The difference was due mostly to increased time LS dams spent nursing pups (LS−LC=9.7±2.1%, P =0.04). Averaged across lactation stages, LS dams tended to spend less time resting with their pups (−2.32±1.04%, P =0.15) than LC dams, but the difference was greatest and significant only in the last stage (−10.45±2.20, P P =0.03). Survival of pups in standardized litters raised by LS dams was 10.4±4.9% greater ( P =0.04) than in standardized LC litters whereas line difference in non-standardized litters was not significant ( P >0.30). Because interactions of line by litter size standardization for maternal behavior traits were not significant, correlated responses in maternal behavior were considered to be independent of size of litter being nursed.

The effect of myostatin genotype on body temperature during extreme temperature events.

Extreme heat and cold events can create deleterious physiological changes in cattle as they attempt to cope. The genetic background of animals can influence their response to these events. The objective of the current study was to determine the impact of myostatin genotype (MG) on body temperature during periods of heat and cold stress. Two groups of crossbred steers and heifers of unknown pedigree and breed fraction with varying percentages of Angus, Simmental, and Piedmontese were placed in a feedlot over 2 summers and 2 winters. Before arrival, animals were genotyped for the Piedmontese-derived myostatin mutation (C313Y) to determine their MG as either homozygous normal (0 copy; n = 84), heterozygous (1 copy; n = 96), or homozygous for inactive myostatin (2 copy; n = 59). Hourly tympanic and vaginal temperature measurements were collected for steers and heifers, respectively, for 5 d during times of anticipated heat and cold stress. Mean (±SD) ambient temperature for summer and winter stress events were 24.4 (±4.64) and -1.80 (±11.71), respectively. A trigonometric function (sine + cosine) with periods of 12 and 24 h was used to describe the diurnal cyclical pattern. Hourly body temperature was analyzed within a season, and fixed effects included MG, group, trigonometric functions nested within group, and interaction of MG with trigonometric functions nested within group; random effects were animal and residual (Model [I]). A combined analysis of season and group was also investigated with the inclusion of season as a main effect and the nesting of effects within both group and season (Model [C]). In both models, the residual was fitted using an autoregressive covariance structure. A 3-way interaction of MG, season, and trigonometric function periodicities of 24 h (P < 0.001) and 12 h (P < 0.02) for Model [C] indicate that a genotype × environment interaction exists for MG. For MG during summer stress events the additive estimate was 0.10°C (P < 0.01) and dominance estimate was -0.12°C (P < 0.001). During winter stress events the additive estimate was 0.10°C (P < 0.001) and dominance estimate was 0.054°C (P > 0.05). The current study illustrated that a genotype × environment interaction exists for MG and 1-copy animals were more robust to environmental extremes in comparison with 0- or 2-copy animals.

Luteinizing hormone and progesterone concentrations in serum of heifers administered a short half-life prostaglandin (PGF2α) or long half-life prostaglandin analogue (fenprostalene) on days six or eleven of the estrous cycle☆

Two trials were conducted to measure the progesterone (P(4)) decline and luteinizing hormone (LH) surge in serum subsequent to administration of a short half-life (short t (1 2 )) prostaglandin (PGF(2alpha)) or a long half-life (long t (1 2 )) prostaglandin analogue (fenprostalene) on Days 6 or 11 of the estrous cycle. Twenty-five crossbred Shorthorn and five Hereford heifers with a mean weight of 331.4 +/- 29.8 kg were used in both trials. The heifers were randomly allotted to receive either a short t (1 2 ) or long t (1 2 ) prostaglandin treatment on Day 6 or 11 of the estrous cycle. A crossover design for the main effect, treatment (type of prostaglandin), was conducted. Heifers that received PGF(2alpha) in Trial I were given fenprostalene in Trial II and vice versa. Stage of the estrous cycle (day) was the same for each heifer in both trials. Stage of estrous cycle was standardized to either Day 6 or 11 by administering Syncro-Mate B (SMB). Blood was collected every hour for 80 h post injection to quantify LH and P(4) concentrations. There were no significant differences (P > 0.05) between the short t (1 2 ) or long t (1 2 ) for either P(4) or LH profiles. In addition, no differences were detected between stages of the estrous cycle for the timing of the preovulatory surge of LH after prostaglandin administration.