Lean Food Research Articles

Selection for components of efficient lean growth rate in pigs 1. Selection pressure applied and direct responses in a Large White herd

AbstractResponses to four generations of divergent selection for lean groivth rate with ad-libitum feeding (LGA), for lean food conversion (LFC) and for daily food intake (DFI) in Large White pigs were studied. The LGA (LFC) selection criterion was designed to obtain equal correlated responses in growth rate (food conversion ratio) and carcass lean content, measured in phenotypic s.d. The selection criteria had phenotypic s.d. of 27, 29 and 253 units, respectively, and results are presented in s.d. units. There was a total of 3537 pigs, with an average of 40 boars and 40 gilts performance tested in each of the high, low and control lines per generation and the lines consisted of 10 sires and 20 dams. The generation interval was equal to 13·5 months. Animals were performance tested in individual pens with mean starting and finishing weights of 30 kg and 85 kg respectively.Cumulative selection differentials in the three selection groups were 5·8, 3·6 and 3·3 phenotypic s.d. for LGA, LFC and DFI respectively. Direct responses to divergent selection were 1·7, 1·3 and 1·2 (s.e. 0·17) for LGA, LFC and DFI. The correlated response in LFC (1·6 (s.e. 0·18)) with selection on LGA was greater than the direct response in LFC. Conversely, the direct response in LGA was greater than the correlated response (1·1 (s.e. 0·18)) with selection on LFC. The response in LFC (–1·1 (s.e. 0·17)) with selection on DFI was similar in size but opposite in sign to the direct response in LFC. Responses were asymmetric about the control, as the high LGA and LFC responses were proportionately smaller (0·74 and 0·58) than low line responses. In contrast, the difference between the high DFI and control was four times greater than the difference between low line and control.Heritabilities of LGA, LFC and DFI were 0·38, 0·35 and 0·29 (s.e. 0·03), when estimated by residual maximum likelihood, with common environmental effects of 0·09 (s.e. 0·02). Genetic correlations for LGA with LFC and DFI were positive, 0·76 (s.e. 0·03) and 0·23 (s.e. 0·07), but the genetic correlation between DFI and LFC was negative, –0·45 (s.e. 0·06). The experiment demonstrated that substantial responses to selection can be achieved in LGA, LFC and DFI. Selection on LGA resulted in larger direct and correlated responses than selection on LFC.

Selection for components of efficient lean growth rate in pigs 4. Genetic and phenotypic parameter estimates and correlated responses in performance test traits with ad-libitum feeding

AbstractGenetic and phenotypic parameters and correlated responses in performance test traits were estimated for populations of Large White (LW) and British Landrace (LR) pigs tested in Edinburgh and Wye respectively, to four generations of divergent selection for lean growth rate (LGA), lean food conversion (LFC) and daily food intake (DFI) with ad-libitum feeding.There were differences between the two populations in genetic parameters, as LW heritabilities for growth rate, daily food intake and backfat depths were higher and the correlation between growth rate and backfat was positive for LW, but negative for LR. However, heritabilities, genetic and phenotypic correlations were generally comparable between selection groups, within each population. Genetic and phenotypic correlations indicated that animals with high daily food intakes were faster growing, had positive residual food intakes (RFI), were fatter with higher food conversion ratios. RFI was highly correlated with daily food intake and food conversion ratio, but phenotypically independent of growth rate and backfat, as expected.Selection for LGA, in LW and LR populations, increased growth rate (54 and 101 g/day), but reduced backfat (−3·9 and −2·0 mm), food conversion ratio (−0·23 and −0·25) and total food intake (−11·8 and −12·6 kg). There was no change in daily food intake in LW pigs (−19 g/day), but daily food intake increased in the LR pigs (69 g/day). With selection for LFC in LW and LR populations, there was no response in groivth rate (9 and 9 g/day), but backfat (−4·1 and −2·1 mm), total (−6·6 and −11·8 kg) and daily food intake (−90 and −172 g) were reduced, as animals had lower food conversion ratios (−0·13 and −0·22). LW and LR pigs selected for DFI ate more food in total (6·8 and 5·9 kg) and on a daily basis (314 and 230 g), grew faster (94 and 51 g/day) and had higher food conversion ratios (0·12 and 0·13). Backfat was increased in LW pigs (3·7 mm), but not in the LR population.In general, efficiency of lean growth was improved by increasing groivth rate, with little change in daily food intake from selection for LGA, but was primarily due to reduced daily food intake with selection on LFC.

Selection for components of efficient lean growth rate in pigs 2. Selection pressure applied and direct responses in a Landrace herd

AbstractResponses to divergent selection for lean growth rate with ad-libitum feeding (LGA), for lean food conversion (LFC) and for daily food intake (DFI) in Landrace pigs were studied. Selection was practised for four generations with a generation interval ofl year. A total of 2642 pigs were performance tested in the high, low and control lines, with an average of 37 boars and 39 gilts performance tested per selection line in each generation. The average within-line inbreeding coefficient at generation four was equal to 0·04. There was one control line for the DFI and LFC selection groups and another control line for the LGA selection group. Animals were performance tested in individual pens with mean starting and finishing weights of 30 kg and 85 kg respectively with ad-libitum feeding. The selection criteria had phenotypic s.d. of 32, 29 and 274 units, for LGA, LFC and DFI, respectively, and results are presented in phenotypic s.d.Cumulative selection differentials (CSD) were 5·1, 4·5 and 5·5 phenotypic s.d. for LGA, LFC and DFI, respectively. Direct responses to selection were 1·4,1·1 and 0·9 (s.e. 0·20) for LGA, LFC and DFI. In each of the three selection groups, the CSD and direct responses to selection were symmetric about the control lines. The correlated response in LFC (1·1, s.e. 0·19) with selection on LGA was equal to the direct response in LFC. In contrast, the direct response in LGA was greater than the correlated response (0·7, s.e. 0·18) with selection on LFC. There was a negative correlated response in DFI (-0·6, s.e. 0·18) with selection on LFC, but the response with selection on LGA was not significant (0·2, s.e. 0·16).Heritabilities for LGA, LFC and DFI ivere 0·25, 0·25 and 0·18 (s.e. 0·03), when estimated by residual maximum likelihood, with common environmental effects of 0·12 (s.e. 0·02). Genetic correlations for LFC with LGA and DFI were respectively positive (0·87, s.e. 0·02) and negative (-0·36, s.e. 0·09), while the genetic correlation between DFI and LGA was not statistically different from zero, 0·13 (s.e. 0·10). Selection on components of efficient lean growth has identified LGA as an effective selection objective for improving both LGA and LFC, without a reduction in DFI.

Selection for components of efficient lean growth in Large White pigs

An experiment was started in 1984 at Edinburgh and Wye to study responses to divergent selection for lean growth rate (LGA), lean food conversion ratio (LFC) and daily food intake (DFI). This paper measured the selection pressure applied, the responses in the selection criteria and estimated the genetic and phenotypic relationships between the selection criteria with ad-libitum feeding of Large White pigs after four generations of selection.Selection objectives and criteria. The LGA (LFC) selection objective was to obtain equal correlated responses in growth rate (food conversion ratio) and carcass lean content, measured in phenotypic s.d. The LGA, LFC and DFI selection criteria had phenotypic s.d. of 27, 29 and 250 units and results are presented in s.d. units.

Responses in performance test traits to selection on components of efficient lean growth

This study determined the responses in performance test traits after four generations of divergent selection for lean growth rate (LGA), lean food conversion ratio (LFC) and daily food intake (DFI) in Large White and Landrace pigs.Within each of the three selection groups, there were high and low selection lines with a control line, each consisting of 10 sires and 20 dams, with an average of 3 boars and 3 gilts tested per litter. A total of 3537 Large White and 2642 Landrace pigs were performance tested in Edinburgh and Wye, respectively. The performance test was over a fixed weight range of 30±3 kg to 85±5 kg. All pigs were individually penned, with ad-libitum feeding of a high energy (13.8 MJ DE/kg DM) and high protein (210 g/kg DM crude protein) pelleted ration.Correlated responses in performance test traits to selection on LGA, LFC and DFI were estimated from the mean within-generation selection line breeding values for each trait, determined with the additive genetic and common environmental (co)variances for performance test traits, which were estimated using multivariate derivative-free residual maximum likelihood analyses.

Reproductive performance of pigs selected for components of efficient lean growth

This study determined the correlated responses in reproductive performance after five generations of divergent selection for components of efficient lean growth rate in Large White pigs.Data were collected from five generations of pigs divergently selected for daily food intake (DFI), lean food conversion (LFC), lean growth rate on ad-libitum feeding (LGA) and lean growth rate on restricted or scale feeding (LGS). In each selection group, there were high, low and control lines, each consisting of 10 boars and 20 gilts. Animals were mated at around 9.5 months of age. Pregnant gilts were fed 2.5 kg daily and farrowed sows up to 3.5 kg twice daily of a 160 g/kg DM crude protein and 132 MJ/kg DM digestible energy ration. Animals were farrowed at 414 (s.d. 19.7) days of age, on average. No cross fostering was practised. Piglets were offered creep feed containing 235 g/kg DM crude protein and 160 MJ/kg DM digestible energy from 14 days and were weaned at an average of 35 (s.d. 3) days. Litter traits were measured on 1220 selected Large White gilts, with 13030 piglet birth weights and 9951 weaning weights.

Selection for components of efficient lean growth in Landrace pigs

To study responses to divergent selection for lean growth rate (LGA), lean food conversion ratio (LFC) and daily food intake (DFI), an experiment was started in 1984 at Edinburgh and Wye. This paper measured the selection pressure applied, the responses in the selection criteria and estimated the genetic and phenotypic relationships between the selection criteria with ad-libitum feeding of Landrace pigs after four generations of selection.The LGA (LFC) selection objective was to obtain equal correlated responses in growth rate (food conversion ratio) and carcass lean content, measured in phenotypic s.d. The LGA, LFC and DFI selection criteria had phenotypic s.d. of 32, 29 and 270 units and results are presented in s.d. units.Boars and gilts were purchased from eight British nucleus herds and boars from national artificial insemination centres in 1982. Homozygous or heterozygous halothane positive pigs were not included in the experiment. The base population consisted of 20 sires and 89 dams. Within each of the three selection groups, there were high and low selection lines with a control line, each consisting of 10 boars and 20 gilts, with a generation interval of one year. There were two control lines, one for LGA and one for LFC and DFI, as selection groups were arrowed continuously. The total number of pigs tested per line and average inbreeding coefficient at generation 4, within selection group are given below.

“Check your 6” — A collaborative effort to teach the base of the food guide pyramid

The Kansas LEAN Food Professionals Task Force is a collaborative group of 15 food and nutrition professionals representing commodity groups, educational entities, private businesses, and the Kansas Department of Health and Environment, that has as its mission to help consumers understand and adopt the principles of the Food Guide Pyramid. The task force chose to begin at the base, with the Bread, Cereal, Rice and Pasta Group. “Check Your 6” was chosen as a title for the campaign because the group hoped to empower consumers to take responsibility for monitoring their progress toward meeting the goals set forth by the U.S.D.A. After identifying multiple target audiences, focus groups were conducted with child care providers, child development specialists, teachers, school food service managers, Extension Home Economists, and Registered Dietitians from across Kansas to determine their perceived needs related to education about the Pyramid in general and this food group in particular. The task force members then determined feasibility of providing requested materials and adopted a plan to develop and produce the chosen components, identify resources to finance the campaign, and provide timelines for production and distribution of materials. Educational packets were developed by the group for child care providers, school and public librarians, fifth-grade teachers, coaches and home economics teachers, school food service managers, and Extension Home Economists. While packets included selected overlapping materials, each contained materials specific to its intended audience designed to result in designated, appropriate learning outcomes for its audience. Over 14,610 packets were distributed nationwide between August 1992 and March 1993. Packets within the state of Kansas were distributed at the expense of the Task Force (over $210,000); printing and shipping costs for out-of-state packets are borne by the users ($1 – $1.50 per packet). Black line masters for all materials are included in packets and materials are in the public domain, encouraging users to reproduce and share the materials. In addition to the educational packets, a 13 1/2 minute video titled “Secrets of the Food Pyramid” was produced and distributed to every school district in Kansas at no charge. The video provides an entertaining introduction to the Food Guide Pyramid with a focus on the base. Young people ride camels to the Pyramid, meet a “magic” individual who shows them how to unlock the secrets of good health, and participate in a supermarket scavenger hunt before returning home to discover the secrets in their own kitchen. Menu contests with school lunch providers rewarded efforts to include a variety of foods within the food group and a recipe contest for home ec students rewarded originality and efforts to reduce fat and include at least four food groups on a sandwich. In addition to campaigns through educational outlets, the task force cooperated with supermarkets in the state to place the “Check Your 6” logo on their grocery sacks, provide consumer cards in their in-store bakeries, include the logo in their ads, and participate in supermarket scavenger hunts with elementary school classes within the state. This cooperation with industry partners to reinforce a specific nutrition message taught in classrooms is unique to this project and is an effective way to integrate nutrition messages into “real world” situations. The Kansas LEAN Food Professionals Task Force has broken new ground in their efforts to assist populations in understanding and adopting the 1990 Dietary Guidelines for Americans. This collaborative effort will continue with development of similar campaigns around fruits and vegetable, using the “5-A-Day” logo, and dairy foods and the protein foods over the next few years.

Grassland performance of Hereford cattle selected for rate and efficiency of lean gain on a concentrate diet

AbstractThe performance of 273 Hereford calves from lines previously selected for lean growth rate (LGR) or lean food conversion efficiency (LFCR), on a concentrate diet, was evaluated on a grassland diet over a period of 3 years. Both bull and heifer calves were tested, and each year the performance test ran from the 1st week of May (average age of 233 days) until the 1st week of October. Carcass lean content was predicted from body weight and ultrasonic backfat depth, and lean gain was calculated from the product of live-weight gain and predicted carcass lean content. The LGR line was superior to the control (C) line for live-weight gain on test, lean gain on test and lean gain from birth until the end of test. The LFCR line performed similarly to the C line for live-weight gain on test and lean gain on test, but was inferior for total lean gain. For lean gain on test, the proportional differences between the lines were similar to those predicted from parental breeding values for LGR, but they were smaller for total lean gain. The lines did not differ significantly for either fat depth or predicted carcass lean content.Heritabilities were high for all growth traits, e.g. 0·52 (s.e. 0·17), 0·54 (s.e. 0·17) and 0·59 (s.e. 0·17) for live-weight gain on test, lean gain on test and total lean gain, but lower for fat depth and carcass lean content, 0·25 (s.e. 0·17) and 0·14 (s.e. 0·16), respectively. Genetic correlations with LGR, measured on a concentrate diet, were 0·57 for lean gain on test and 0·56 for total lean gain. If only males were considered, these correlations rose to 0·80 and 0·70, respectively. Coheritabilities between the two environments for lean growth were close to 0·3. It is concluded that although there is some evidence for genotype × environment and genotype × sex interactions, selection for lean growth on a concentrate regimen will still be effective in improving grassland performance.

Genetic variation in measures of food efficiency in pigs and their genetic relationships with growth rate and backfat

AbstractData on 3783 Yorkshire, 2842 Landrace and 937 Duroc littermate pairs of boars, station tested between 1976 and 1989, were used to measure genetic parameters of average daily gain (ADG) from 30 to 90 kg, live backfat at 90 kg (BF), estimated lean growth rate (LGR), average daily food intake, food conversion ratio (FCR) and lean food conversion ratio (LFCR), as well as measures of residual daily food intakes over and above requirements for growth and lean growth. A method was developed to obtain restricted maximum likelihood estimates of genetic variances and covariances under an animal model when observations are on the means of sib pairs. Heritabilities of ADG, BF, LGR, FCR and LFCR were 0·43, 0·59, 0·39, 0·28 and 0·34, respectively. Heritability of daily food intake was 0·45, and heritability of measures of residual daily food intake ranged from 0·30 to 0·38. About half of the variation in daily food intake was residual (0·48 to 0·56). Genetic correlations of ADG with daily food intake, FCR and LFCR were 0·80, −0·28 and −0·09, respectively, and were small and positive (0·18 to 0·34) with measures of residual daily food intake. Backfat had genetic correlations of 0·42, 0·24 and 0·52 with daily food intake, FCR and LFCR, respectively, and genetic correlations between backfat and measures of residual daily food intake ranged from 0·15 to 0·61. Selection against residual food intake may be a useful means of improving efficiency of food utilization.

The performance of Hereford × Friesian offspring of bulls selected for lean growth rate and lean food conversion efficiency

AbstractThe performance of Hereford × Friesian calves sired by Hereford bulls selected for either lean growth rate (LGR) or lean food conversion ratio (LFCR), or by unselected Hereford bulls, was evaluated on 327 calves on three farms over 2 years. Animals started test at 130 days of age on average and remained on test for approximately 300 days, whereupon all animals were slaughtered and carcass dissections were undertaken. Individual food intake was measured on tioo of the farms (189 animals), but only intake per pen of animals was measured on the third farm and individual food intake had to be estimated. LGR, LFCR and other traits describing performance were calculated from the growth, food intake and carcass composition data.If no breed or environment interactions exist it is expected that proportionately 0-5 of the genetic differences between selected and control line bulls would be transmitted to their offspring. For the LGR and LFCR line bulls these values were 0·38 and 0·44, respectively, however the LGR value had a much smaller confidence interval. Genetic correlations derived from regressing breeding values predicted from offspring performance on breeding values predicted from the bulk's own performance in the selection experiment were 0·62 (s.e. 0·28) and 0·96 (s.e. 0·28) for LGR and LFCR, respectively. Heritabilities were: live-weight gain on test, 0·27; daily gain, 0·48; food intake, 0·06; food conversion ratio, 0·46; predicted carcass lean content, 0·10; killing-out proportion, 0·10; LGR, 0·36 and LFCR, 0·48.

Blood metabolite concentrations in Hereford x Friesian offspring of bulls selected for lean growth rate and lean food conversion efficiency

SummaryBlood samples were taken at intervals from 5 to 13.5 months of age on 352 Hereford x Friesian calves undergoing a postweaning performance test. Up to 5 samples were taken on each animal. The calves were sired by bulls selected for either Lean Growth Rate (LGR) or Lean Food Conversion Ratio (LFCR), or by unselected bulls acting as controls. Measurements taken on the blood samples were concentrations of total blood protein, albumin, urea, β‐hydroxy butyrate, glucose and haemoglobin. Albumin was subtracted from total blood protein to give globulin concentrations.Significant between line differences were observed only for globulin, with the LGR calves having higher concentrations and the LFCR calves lower concentrations than the control calves. Heritabilities for protein, albumin, globulin, urea, β‐hydroxy butyrate, glucose and haemoglobin concentrations were 0.18, 0.09, 0.14, 0.12, 0.00, 0.07 and 0.23, respectively. All metabolites, except β‐hydroxy butyrate, showed a significant repeatability between successive measurements taken on indivudual animals, but for haemoglobin concentrations the estimated repeatability was lower than the heritability. Genetic correlations between the metabolite concentrations and LGR and LFCR mirrored the LGR, LFCR and control line means for urea, glucose and haemoglobin concentrations, but no correlations were significantly different from zero. No strong relationships were observed between performance traits and any of the blood measurements, and only for carcass composition traits did indexes of blood measurements account for more than 0.01 of the total variation.ZusammenfassungBlutmetaboliten‐Konzentration bei Hereford/Friesennachkommen von Selektionslinien für Magerfleischzuwachs und Magerfleisch‐FutterverwertungBlutproben wurden zwischen 5 und 13½ Monaten von 352 Hereford/Friesen während Leistungsprüfung gezogen (bis zu 5 Proben je Tier). Die Väter waren aus Linien, die entweder für Magerfleischzuwachsrate (LGR) oder Magerfleisch‐Futterumwandlung (LFCR) selektiert wurden oder von Kontrollen. Es wurden Blutkonzentrationen für Gesamtprotein, Albumin, Harnstoff, β‐Hydroxylblutyrat, Glukose und Hämoglobin bestimmt. Albumin wurde vom Gesamtblutprotein zur Bestimmung von Globulin abgezogen.Signifikante Unterschiede zwischen Linien waren nur bei Globulin vorhanden, wobei LGR Tiere höhere und LFCR Tiere niedrigere Konzentrationen als die Kontrollen hatten. Heritabilitätswerte für Protein‐, Albumin‐, Globulin‐, Harnstoff‐, β‐Hydroxylbutyrat und Hämoglobin‐Konzentrationen waren 18, 9, 14 und 12, 0, 7 und 23%. Alle Metaboliten mit Ausnahme von β‐Hydroxylbutyrat zeigten signifikante Wiederholbarkeit zwischen aufeinanderfolgenden Bestimmungen, wobei Hämoglobin kleinere Wiederholbarkeit als Heritabilität zeigte. Genetische Korrelation zwischen Metaboliten‐Konzentration und LGR bzw. LFCR widerspiegelten die Linien‐Mittelwerte für Harnstoff, Glukose und Hämoglobinkonzentrationen, jedoch waren keine von diesen signifikant von 0 verschieden. Es wurden auch keine engen Beziehungen zwischen Leistungsmerkmalen und den Blutmaßen festgestellt, und nur für Schlachtkörperzusammensetzung haben die Blutwerte mehr als 1% der Gesamtvarianz verursacht.

Phenotypic and genetic variation in body weight, food intake and energy utilisation in Hereford cattle I. Performance test results

From body weight, food intake and carcass composition data on 542 Hereford bull calves, measuredfrom 200 to 400 days, several traits relating to the efficiency of beef cattle production were derived and analysed. Traits included body weight at various ages, weight gain, predicted carcass lean content, lean growth rate, food intake, food conversion ratio, lean food conversion ratio, food intake in relation to metabolic body weight, energy required for protein and fat deposition, and predicted maintenance expenditure. Maintenance expenditure and the costs of fat and protein deposition were calculated by two means,firstly from allometric equations describing fat and protein accretion, and secondly from a multiple regression of food intake on weight gain and predicted carcass lean content. The two methods gave different mean values, but the correlations between traits calculated by the two methods were almost all 1.00. Exponents for metabolic body weight derived from the two methods were 0.738 and 0.758, respectively. Genetic parameters were calculated using multivariate Restricted Maximum Likelihood techniques.Body weight, carcass composition and traits combining these measurements were moderately to strongly inherited whereas traits related to food intake and efficiency were weakly to moderately inherited. Energy used to deposit fat and lean was more strongly inherited than predicted maintenance expenditure, and these traits were genetically almost uncorrelated. Maintenance energy expenditure showed no genetic relationship with predicted carcass lean content. Efficiency and predicted maintenance expenditure were favourably correlated.

Phenotypic and genetic variation in body weight, food intake and energy utilisation in Hereford cattle II. Effects of age and length of performance test

The effects of length of test, age when evaluations are made, and correction of data for body weightat the start of test on genetic and phenotypic parameters describing performance test results in beef cattle were studied. The data consisted of body weight, food intake and carcass composition measurements on 542 Hereford bull calves, from 200 to 400 days of age. The traits studied included weights at various ages, weight gain, lean growth rate, food intake, food conversion ratio, lean food conversion ratio, food intake in relation to metabolic body weight, energy required for protein and fat deposition, and predicted maintenance expenditure. Traits were derived for the whole test as well as for part test periods of 200–300 days and 300–400 days. Heritabilities for all traits, except those describing weight at a given age, were lower for the 300–400-day period than for either the 200–300-day period or the whole test. Correlations, however, were higher between whole test and 300–400-day traits than between whole test and 200–300-day traits. Phenotypic correlations between the same trait measured in the two-part test period were very low and much lower than the genetic correlations. Corrections for body weight at the start of test had only a trivial effect on the heritabilities of all traits, the relationships between traits and potential genetic progress in traits measured during the test.

Utilization of the sex-determining region Y gene in beef cattle breeding schemes

AbstractIn mammals ‘maleness’, i.e. the presence of testes, is thought to be controlled by a single gene on the Y chromosome. Recently, a candidate gene termed the SRY (sex-determining region Y) gene has been located. If the SRY gene is the gene causing maleness then a transgenic male with the SRY gene on an autosome would produce a greater proportion of male offspring than a normal male. This would be advantageous in situations where male offspring are more valuable than females. Such transgenic males have a reduced probability of propagating their genotype and an effort has to be made to avoid their extinction. This is at the cost of genetic progress which must be made to enable the transgenics to remain competitive with normal males.In a simulated beef cattle breeding scheme if half of the annual matings were made to transgenics then after 15 years of selection the transgenic males fell the equivalent of 2·6 years of selection behind males in a traditional herd. If all matings were made to transgenics they fell over 9 years behind. Selection for lean food conversion ratio was considered as an example. After 15 years of selection the gain in biological efficiency from more male offspring outweighed the loss from reduced genetic progress only when more than 0·5 of the bulls used in the breeding scheme were normal males. In practice, the difficulty of maintaining a small population of transgenic males along with other costs not included in the calculations suggest that breeding schemes in beef cattle with an SRY transgene would not be practicable without further technology.

Selection for rate and efficiency of lean gain in Hereford cattle. 2. Evaluation of correlated responses

ABSTRACTCorrelated responses in two lines of Hereford cattle selected for lean growth rate (LGR) from birth to 400 days of age and lean food conversion ratio (LFCR) from 200 to 400 days of age for a period of 8 years were evaluated. Correlated changes were estimated by two methods: deviation of selected lines from a control line and restricted maximum likelihood. Generally, estimates from the two methods were similar but tended to be more precise for the latter. Statistically significant correlated responses occurred in growth rate in the LGR line and in lean proportion and food conversion ratio in both selected lines. Selection for LGR was accompanied by increases in body weight at various ages in both male and female progeny. In the LFCR line there were little or no changes in body weight for male calves but some increases at certain ages for female progeny. There were no adverse correlated responses detected in reproductive traits such as calving difficulty and calving and pre-weaning mortality.

Selection for rate and efficiency of lean gain in Hereford cattle 1. Selection pressure applied and direct responses

ABSTRACTSelection of bulls for rate and efficiency of lean gain was studied in a herd of Hereford cattle. There were two selection lines, one selected for lean growth rate (LGR) from birth to 400 days and the other for lean food conversion ratio (LFCR) from 200 to 400 days of age, for a period of 8 years. A control line bred by frozen semen from foundation bulls was also maintained. Generation interval was about 2·4 years and average male selection differentials, per generation were 1·2 and — 1·1 phenotypic standard deviation units for LGR and LFCR respectively.Genetic parameters and responses to selection were estimated from the deviation of the selected lines from a control line and by restricted maximum likelihood (REML) techniques on the same material. Realized heritabilities were 0·40 (s.e. 0·12) for LGR and 0·40 (s.e. 0·13) for LFCR using the control line. Corresponding estimates from REML were 0·42 (s.e. 0·10) and 0·37 (s.e. 0·14). The estimate of the genetic correlation between LGR and LFCR was about — 0·69 (s.e. 0·12) using REML.The estimates of direct annual genetic change using deviations from the control were 3·6 (s.e. 1·3) g/day for LGR and — 0·14 (s.e. 0·07) kg food per kg lean gain for LFCR. Corrsponding estimates from REML were similar but more precisely estimated. The correlated responses for LFCR in the LGR line was higher than the direct response for LFCR.

Effect of food intake capacity on production traits in growing pigs with restricted feeding

ABSTRACTEffects of food intake (FI) and ad libitum food intake capacity (FIC) were investigated in 438 pigs fed in seven batches. Batches 1 to 6 consisted of barrows and batch 7 of gilts. Restrictedly fed animals had one to three ad libitum fed litter mates. In batches 6 and 7, animals were fed ad libitum until 48 kg live weight. Thereafter, two-thirds of the animals were fed according to a fixed weight scale. FIC is considered as a trait of the animal, independent of its actual FI. With ad libitum feeding FIC can be measured directly, with restricted feeding FIC has to be estimated.Two methods of estimating average FIC from about 27 to 107 kg live weight were applied. The first method consisted of assigning to each restrictedly fed animal the average FI of one to three ad libitum fed litter mates. The second method was applied in batches 6 and 7 only and consisted of estimating FIC with multiple regression based on individual 'ad libitum performance' in the first part of the growing period.Effects of FI and FIC on daily gain, food conversion ratio, backfat thickness, lean tissue proportion, fatty tissue proportion, lean tissue growth rate, fatty tissue growth rate and lean tissue food conversion were investigated. FI had significant effects on each trait, except on lean tissue food conversion. FIC had significant effects on body composition traits, but not on daily gain and food conversion ratio.Irrespective of the method used to estimate FIC, results showed that animals with a higher FIC produced more fat and less lean from the same amount of food than animals with a lower FIC. It was suggested that the partition of food energy between energy for maintenance, protein deposition and fat deposition is associated with FIC. The findings confirmed that selection for leaner and more efficient pigs may result in animals with lower FIC, irrespective of the feeding regimen during performance testing.

Differential rates of genetic change and genotype × environment interactions in six pig breeding company populations and a purebred Large White population

ABSTRACTDifferential rates of genetic change in litter productivity, growth and carcass traits were estimated for the pig populations of six British breeding companies from their relative performance between 1972 and 1981 in the Meat and Livestock Commission's Commercial Pig Evaluation. Pigs were grown on one of two feeding regimens and slaughtered at one of three live weights (61, 93 and 118 kg).Important differentials were found for a number of traits. Annual rates of change in litter size at birth differed by 0·34 pigs between the two extreme populations. The range between populations for live-weight daily gain (ad libitum feeding) was 20 g, for lean weight daily gain (restricted feeding) it was 6 g, and for lean weight food conversion (feeding regimens pooled) it was 28 g food per g gain. The average annual rate of change of the six company populations was compared with the rate achieved by the purebred Large White breed over the period 1972 to 1977. For mean piglet birth weight the rate was 30 g higher for the company populations, whilst for carcass weight daily gain it was 24 g higher.There was little evidence for population × feeding regimen interactions except that companies ranked differently in average daily food intake, live-weight daily gain and carcass weight daily gain on the two feeding regimens. On limited evidence, population × slaughter weight interactions were also unimportant.

Effect of average daily food intake on production performance in growing pigs

ABSTRACTEffects of daily food intake (FI) on daily gain (DG), food conversion ratio (FCR), ultrasonic backfat thickness (BF), proportion of lean parts (LP), proportion of fatty parts (FP), lean tissue growth rate (LTGR), fatty tissue growth rate (FTGR) and lean tissue food conversion (LTFC) were investigated in 687 barrows and 98 gilts, slaughtered at a mean live weight of 108 kg and fattened in seven batches. In the range of food intake from about 1·7 to 3·2 kg/day (22 to 42 MJ digestible energy) a continuous distribution of data was available.Body composition was linearly related to FI. Most regressions of BF and all of LP and of FP on FI were linear, showing fatter animals at higher food intake. For FTGR, BF, LP and FP, parameter estimates based on linear regression were given. Although the response of DG and of LTGR on increasing FI was not always significantly different from linearity, the second degree polynomials indicated diminishing returns in all batches. FTGR had a high linear correlation with FI (0·85 to 0·95), indicating that in the present range of FI a rather fixed proportion of the food was used to deposit fatty tissue.For DG and LTGR a non-linear model of the type a(FI -fo)bwas fitted, wherefowas interpreted as maintenance requirement. For FCR and LTFC the corresponding model was FI/(α(FI —fo)b). Both models were preferred over second degree polynomials because of better interpretation of parameters. FCR and LTFC showed minima at about 2·6 and 2·2 kg/day food intake, but especially for FCR the increase at increasing FI was low. Results were not consistent in demonstrating or refuting a plateau in LTGR, which in any event appears to lie near to or beyondad libitumFI for most pigs.