Lamb production and its components in pure breeds and composite lines. II. Breed effects and heterosis

Ewe performance was compared for five pure breeds of sheep (Finnsheep, F; Rambouillet, R; Dorset, D; Targhee, T; Suffolk, S) and the crosses in development of two maternal composite lines (C1 = 1/2F1/4R1/4D and C2 = 1/2F1/4T1/4S). The data involved 10,959 breeding season records of 4,219 ewes by 412 sires. Ewe production and the components (fertility, litter size, neonatal and preweaning lamb survival and mean lamb weaning weight) were adjusted for age and standardized across season of lambing and years. The D and F ewes produced more weight of lamb/ewe exposed than R, S and T ewes because of higher D and F fertility, higher D lamb survival and larger F litters. First cross and inter se generations of C1 and C2 ewes averaged 17 to 27% higher fertility than the parental mean. Litter size averaged about one lamb higher for F than for other pure breeds, but only slightly higher for C1 and C2 than for the mean of F and other breeds. Lower neonatal survival for F than for other breeds and crosses was associated with the larger F litters and with 2 to 8% positive heterosis in the crosses. Preweaning survival of suckled and nursery lambs was low for F and S and positive heterosis ranged from 9 to 19% in crosses. Mean lamb weaning weights were highest for S, lowest for F, with little heterosis in crosses. Crossbred ewes reared .3 to .4 more lambs than mean for parental pure breeds. Heterosis in C1 and C2 ranged from 11 to 28% for lambs born, 27 to 43% for lambs weaned and 29 to 44% for weight of lamb weaned/ewe exposed. Decline in heterosis with inter se mating of crosses was no greater than expected from the reduction in predicted heterozygosity.     

Composition of the whole body and component fractions in mature ewes from seven breeds

In a sheep production system, effects of body composition on nutrient requirements for maintenance, tissue deposition and lean meat production may be important. Composition of body fractions differing in expected metabolic activity was measured for 12 nonpregnant, nonlactating, 3- to 4-yr-old ewes from each of seven breeds representing diverse body size and performance characteristics. Half the ewes in each breed had ad libitum access to feed and half were fed at maintenance levels for an average of 41 d. Ewes were slaughtered after a 72-h fast. Empty bodies were divided into visceral organs and blood (ORB); gastrointestinal tract and internal fat (GIF); head, hooves and pelt (HHP); and carcass (CAR). Water, fat, ash and the remaining fat-free dry organic matter (FFDOM) contents were determined for each fraction. Mean empty body weight (EBW) was 60.8 kg and mean composition was 47.6% water, 34.1% fat, 14.8% FFDOM and 3.5% ash. Among breeds, larger mature size generally was associated with a higher percentage of fat and a lower percentage of water (P less than .01), in agreement with carcass composition. Ewes with ad libitum access to feed had more fat and less water in their EBW than did those fed at maintenance levels, especially in the GIF fraction. Distribution of EBW averaged 58.1%, CAR, 19.0%, GIF, 15.4% HHP and 7.5% ORB. The larger, faster growing breeds had the highest proportion of the EBW and of each chemical component located in the carcass. The smaller, more prolific breeds had the highest percentages of EBW in the ORB and GIF fractions. Effects of these large genetic differences in body composition and tissue distribution on production efficiency need to be evaluated.     

A deterministic computer simulation model of life-cycle lamb and wool production.

A deterministic mathematical computer model was developed to simulate effects on life-cycle efficiency of lamb and wool production from genetic improvement of performance traits under alternative management systems. Genetic input parameters can be varied for age at puberty, length of anestrus, fertility, precocity of fertility, number born, milk yield, mortality, growth rate, body fat, and wool growth. Management options include mating systems, lambing intervals, feeding levels, creep feeding, weaning age, marketing age or weight, and culling policy. Simulated growth of animals is linear from birth to inflection point, then slows asymptotically to specified mature empty BW and fat content when nutrition is not limiting. The ME intake requirement to maintain normal condition is calculated daily or weekly for maintenance, protein and fat deposition, wool growth, gestation, and lactation. Simulated feed intake is the minimum of availability, DM physical limit, or ME physiological limit. Tissue catabolism occurs when intake is below the requirement for essential functions. Mortality increases when BW is depressed. Equations developed for calculations of biological functions were validated with published and unpublished experimental data. Lifetime totals are accumulated for TDN, DM, and protein intake and for market lamb equivalent output values of empty body or carcass lean and wool from both lambs and ewes. These measures of efficiency for combinations of genetic, management, and marketing variables can provide the relative economic weighting of traits needed to derive optimal criteria for genetic selection among and within breeds under defined industry production systems.     

Selection for postweaning gain in rats: III. Correlated response in maternal performance

Effects from 34 generations of selection, either up (U) or down (D), for 3- to 9-wk weight gain on genetic direct and postnatal maternal effects, dam size and maternal efficiency were evaluated in 25 cross-fostered sets of rats. Direct genetic effects on 12-d pup weight were 14 and 9% above controls (C) for U and D lines, respectively (P less than .01). Postnatal maternal effects on 12-d pup weight were also 11% higher for the U line (P less than .01), but not different from C for the D line. Females of the U line were heavier (P less than .01) by 13% at mating, 12% at parturition and 15% at 12 d of lactation, relative to controls. They also produced 11% greater total litter weight at 12 d and consumed 9% more feed, but were only nonsignificantly lower in feed per unit of pup 12-d litter weight. Females of D line were -8, -7 and -3% relative to controls in the three weights, but did not differ from controls in 12-d litter weight, feed consumed or in feed efficiency during lactation.     

Simulated effects of reproductive performance on life-cycle efficiency of lamb and wool production at three lambing intervals.

A deterministic computer model of a purebreeding sheep production system was used to simulate effects on life-cycle efficiency from genetic changes in lambing rate (LB), fertility (FERT), precocity of fertility (PREC), and estrus season length (ES) under annual (Y), 4-mo (A), and 73-d (S) breeding intervals. Ewes and lambs of a 1,000-ewe flock were fed to requirement through five yr, beginning with ewe lambs at the optimal breeding season and accumulating feed input (TDN) and market lamb equivalent weight of output (EBW), including cull ewes and wool. For annual lambing, improvement in cost (TDN/EBW equivalence) per 10% increase in genetic potential was -9.8, -8.2, -1.3, and -.8% for LB, FERT, PREC, and ES, respectively. For the A and S lambing intervals, corresponding gains in TDN efficiency were -19 for FERT and -9% for LB when ES was 72 d, but only -6 and -5% when ES was 192 d. Increasing PREC by 10% improved cost -3% under accelerated systems when ES was 72 d, but less than -1% when ES was 192 d. Cost reduction from 10% longer ES under A and S breeding intervals was greater when other reproductive performance was low (-11 and -17%) rather than high (-2 and -3%). Reduction in costs for A and S vs Y lambing intervals was greatest with long ES and was greater with low (-43 and -53%) than with high reproductive performance (-20 and -24%). When ES was 72 d, A and S intervals would reduce costs for high (-9 and -11%) but increase costs for low reproductive traits. Corresponding increases in CP/TDN required in diet would reduce gains in TDN/EBW only slightly. These results should aid in development of optimum selection criteria for stocks used for pure or rotation crossbreeding or as maternal parents of terminal crosses.     

Web-based, interactive simulation of an anesthesia machine

Gases are transparent and the piping layout in anesthesia machines is not obvious, making it hard to understand anesthesia machine function, potential failure modes, and recovery from faults. We experimented with an approach that simplified the layout of the anesthesia machine piping by removing extraneous details and making gases not only visible, but also color-coded. More than 15 anesthesia machine controls were represented by icons that a user can adjust by clicking on the icon with a pointing device and subsequently observing the effect of his/her intervention on anesthesia machine function in real time. We simulated two anesthesia machine failures and also supported non-English languages and non-US gas color codes. Further, we initiated an experiment in Web philanthropy by deliberately choosing to make the educational module accessible without charge and selected the Web as the preferred medium for dissemination of the Virtual Anesthesia Machine (VAM) viewable at http://www.anest.ufl.edu/vam . Originally designed for use in human anesthesiology, a significant percentage (about 30%) of the 54 000 international visitors, as tracked by an independent third-party Web traffic monitoring service, for the period 9/00–5/02, were from the veterinary field. VAM is being used as part of the curriculum in veterinary programs in the US and overseas and has been well received by the global anesthesia community (human and veterinary).     

Energy utilization in mature ewes from seven breeds with diverse production potentials

Effects of genetic changes in reproduction, growth, body composition or lactation on the efficiency of market lamb production depend partly on the associated changes in feed intake requirements for maintenance and for protein and fat deposition. To evaluate these relationships, feed intake and body weight changes were monitored for six pairs of open, dry, mature ewes from each of seven diverse breeds fed pelleted alfalfa (53% TDN) ad libitum (AL) or restricted (MN) to 64% of ad libitum levels, for an average of 41 d. After a 56-h fast, heat production (FHP) was measured calorimetrically for 16 h before slaughter and analysis of empty body composition. The estimated daily metabolizable energy intake/kg(.75) of body weight for no change in body energy (MEm) was 167 kcal for the AL vs 147 kcal for MN ewes, and ranged from 139 to 169 among breeds (P less than .05). Estimated above-maintenance ME requirements, kcal/g tissue deposited, were 30 to 50 for protein and 10 to 14 for fat deposition. Mean FHP/d, adjusted by regression to zero activity, was 72 kcal/kg(.75) weight and was nonsignificantly higher (3.3) for the leaner MN than for AL ewes. Thus, the lower total MEm for MN than for AL ewes was necessarily derived from reduced metabolic and physical activity and(or) higher digestibility. Genetic increases in lean vs fat deposition would reduce above-maintenance feed by one-third to one-fourth because of the high water content of lean, but more lean mass may increase maintenance costs.