There is certainly nothing new in saying that inbreeding, the mating of related individuals, has negative consequences in farmed animal populations. Inbreeding leads to loss of genetic variation and most importantly to reductions in performance (i.e. inbreeding depression) particularly in traits related with fitness such as fertility and viability. Reductions in fitness traits can eventually make further progress imposible despite the presence of genetic variance. Even large populations are experiencing large increases in the rates at which inbreeding accumulates. Examples include US and UK Holstein dairy cattle populations where the worldwide use of few elite sires is leading to current rates much higher than those observed in the past and where deteriorations in health and reproductive traits have been observed. Broadening the breeding objectives for livestock species (Simm et al., 2001) would alleviate this but still effective methods for controlling inbreeding need to be applied.

Abstract Increased rates of inbreeding are one side effect of breeding programmes designed to give genetic progress for traits of economic importance in livestock. Inbreeding leads to inbreeding depression for traits showing dominance, and will ultimately lead to a decrease in genetic variance within populations. Here we review theoretical and experimental literature from animal breeding, evolutionary biology and conservation genetics on the consequences of inbreeding in terms of trait means and genetic and environmental variance components. The genetic background for these effects is presented and the experimental literature interpreted in relation to them. Furthermore, purging of deleterious alleles and the variable nature of effects of inbreeding on populations are discussed. Based on the literature, we conclude that inbreeding in animal breeding must be controlled very efficiently to maintain long-term sustainable livestock production in the future. The tools to do this efficiently exist, and much can be learnt on inbreeding from the literature in fields only distantly related to animal breeding.

The confirmation of the segregation of experimentally populations is required before their commercial design of such confirmation experiments has the the pedigree while maintaining the power to detect chromosomes of a complex pedigree of 570 Charollais contained a moderately sized half-sib family which was wide level were detected in the half-sib analysis and analysis of the complex pedigree using identity-by-estimation of QTL effects was achieved by fitting all observed in the single QTL models. Both methods of different regions, and the variance components method demonstrates the viability of applying a variance inbreeding.

This study investigated traits that could be used to aid selective breeding for increased nematode resistance in sheep. Data were collected on approximately 1000 Scottish Blackface lambs over a 5-year period (1992–6). The animals were continually exposed to mixed nematode infection by grazing. Anthelmintic treatment was administered and blood samples were collected every 28 days from 4 to 24 weeks of age. Approximately 500 of the lambs were necropsied at 6 to 7 months of age and their worm burdens were recorded. The traits measured were the number of adult males, adult females, fifth-stage larvae and fourth-stage larvae for all species present. In addition, the mean length of adult females and the number of eggs in utero were estimated for Teladorsagia circumcincta. Several indicator traits were also measured on some of the animals, including : faecal egg counts, immunoglobulin A activity and eosinophil count as markers of the local immune response, and plasma pepsinogen activity and fructosamine concentration as indicators of the pathological consequence of infection. The heritabilities for worm length, eggs in utero and worm burden were 0.53±0.17, 0.50±0.16 and 0.13±0.10 respectively. At a mean age of 22 weeks the heritabilities for fructosamine concentration, IgA activity, eosinophil count and pepsinogen activity were 0.39±0.16, 0.57±0.15, 0.35±0.15 and 0.56±0.16 respectively. Strong negative genetic correlations (< −0.6) were often observed between necropsy traits and eosinophil count, IgA activity and pepsinogen activity. Substantial genetic correlations were also observed between fructosamine concentration and worm length (0.67) and number of fourth-stage larvae (−0.80). The genetic and environmental correlations between indicators and necropsy traits were often opposite in sign. The indicator traits studied could aid selection for increased resistance to gastrointestinal nematodes in sheep.

The objective of the present study was to compare growth curves for live weight (LW) and body size of three strains of female dairy cattle reared under common environments in Ireland. One strain (HP) was selected from a predominantly North-American/European Holstein-Friesian genetic pool selected for high milk production. The second strain (HD) represented a predominantly North-American/European Holstein-Friesian genetic pool selected for high milk production but with greater selection emphasis on functional non-production traits. The third strain (NZ) consisted of New Zealand Holstein-Friesian females of high genetic merit for profitability in New Zealand. The data consisted of 99 animals (33 animals in each strain) with records on LW, length, girth and height from birth to a minimum of 594 days of age. The von Bertalanffy growth function was fitted to each animal's records separately and least-squares analyses were used to investigate the effect of strain on birth LW/body size, parameters of the growth function and average daily gains. Average mature live weight of the HD animals (591 kg) was significantly larger than that of the HP (566 kg) or NZ (543 kg) strain; the HD strain matured more slowly. The HD (134 cm) and HP (135 cm) strains were significantly taller than the NZ (128 cm) strain. Although the data set was relatively small there are indications that dairy females of North-American genetic origin were heavier at birth, grew faster, and were heavier and taller at maturity than dairy females of New Zealand origin.

A total of 166 crossbred young female rabbits were used to study the effect of two types of crossbred does (H1 v. H2, old and current generations, respectively) from the cross of different generations of maternal lines selected for litter size, the use of a feeding programme based on a low energy rearing diet (F) and the presentation of a high-energy diet pre-partum (E) on the performance of young rabbit females until their first parturition and on the main litter traits at first kindling. Perirenal fat was thicker at the age of 3 months for H2 than for H1 does, but this difference disappeared at the first insemination (4·5 months). H2 does had a significantly larger total number and number of live pups at birth (+2·06 live pups) than H1, higher than expected (+1·06). As this greater foetal growth was obtained for a similar energy intake of does, possible differences may exist in partitioning and/or effficiencies of dietary and body energies in favour of foetal growth as the genetic propensity for litter size increased. The use of a low-energy diet significantly reduced the growth of does during the rearing period (−294 g), but they showed a greater compensatory growth during the first 4 weeks of gestation (+79 g) as a consequence of their higher energy intake, without any retardation in their reproductive development. Does receiving diet F until 28th day of gestation showed a significantly greater pre-partum energy intake and their number of pups born alive was lower (−1·3 pups). Finally, the litters of females receiving diet E pre-partum and during lactation had lower mortality during the 1st week (26·9 v. 42·9% dead pups) and throughout lactation than those receiving a moderate energy diet.

The objective of this study was to assess the effect of dietary saponins, extracted from the plant Quillaja saponaria, on the concentrations of immunoglobulins in sow colostrum and milk, and additionally to observe any effect on piglet performance. Twenty-two sows were allocated to each of two dietary treatments on day 72 of gestation, balancing for parity, fatness and past reproductive performance. Treatments were : control (C) and supplemented (Q; 2.5 g saponin per day as a top-dressing). Sows received 2.5 kg food once per day throughout gestation. Between days 72 and 93 of gestation Q sows received a saponin top-dressing as described. After day 93, all sows were given the same diet and managed in an identical manner. Colostrum samples were taken from all sows at farrowing on delivery of the first piglet then 4, 8, 24 and 72 h later and again on day 21 of lactation. A group of eight sows from each treatment were also blood sampled at farrowing, day 3 and day 21 of lactation. Concentrations of immunoglobulins IgG and IgA in the colostrum, milk and blood were not affected by sow treatment during gestation at any sampling point. Fat, lactose and cell counts were also similar across treatments in colostrum and milk. Protein tended to be higher in milk on day 3 but lower on day 21 (P < 0.1) in Q sows. Piglet performance was not affected by sow treatment during week 1 of lactation. However pigs suckling Q sows grew more slowly between days 8 to 14 (P < 0.05) and days 15 to 21 (P < 0.1). Q sows also had fewer stillborn piglets in their litters at farrowing (7.67 v. 13.25%, P < 0.05, s.e. = 1.93). It is concluded that dietary quillaja saponin given during this time period has no influence on sow lacteal immunoglobulin secretions. However an adverse effect on performance of the sucking piglet was observed, the reasons for which are unclear, but may be related to reduced milk protein concentrations. Dietary quillaja saponin during gestation does however appear to reduce the incidence of stillborn piglets.

The influence of the physical structure level in the diet on animal performance was investigated in 52 Belgian Blue doublemuscled bulls starting from a live weight of 348 kg until slaughter at about 645 kg. Four diets with different concentrate/maize silage ratios were offered ad libitum. The structural value (SV), developed in Belgium as a measure of physical structure in the diet for dairy cows, amounted to respectively 0.63 (HSV; high SV), 0.54 (MSV; moderate SV), 0.43 (LSV; low SV) and 0.34 (VLSV; very low SV) per kg dry matter.

Growth rate, food intake and food conversion were all linearly affected by the decreasing SV of the diet. Among carcass parameters only the SEUROP conformation score showed a significant effect of the SV, with the MSV group having the highest score and VLSV the lowest. No important influence of the SV on the histological damage of the ruminal papillae or on the foot lesions was found.

Based on the lower growth rate and food intake of the LSV group versus the HSV group, a SV of the diet between 0.54 and 0.43 is considered as an absolute minimum for Belgian Blue double-muscled bulls.

Two experiments were carried out to examine the effects of the timing and duration of mineral supplementation of the ewe's diet in the final 6 weeks of gestation on immunoglobulin G (IgG) absorption by their progeny. In experiment 1, 60 single-bearing ewes were allocated to one of four dietary treatments (no. = 15) and offered a basal diet of grass silage ad libitum, containing 50 g/kg molassed sugar-beet pulp, which was supplemented with concentrates for the final 7 weeks of pregnancy and were additionally provided with a daily mineral/vitamin supplement for the final 6 weeks (W-6), 4 weeks (W-4), 2 weeks (W-2) or no mineral/vitamin supplement, (control; W-0). The supplement contained Ca, P, Na, Mg, Mn, Zn, Se, Co, I and vitamin E and was offered at the daily rate of 48 g per ewe. The ewes were milked at 1, 10 and 18 h post partum and measured quantities of colostrum, proportional to birth weight were fed back to the progeny via a stomach tube. At each milking, colostrum yield was recorded and colostrum samples taken to determine the concentration and yield of IgG. Treatment had no effect (P > 0.05) on the yields of colostrum or IgG to 18 h post partum. The efficiency of IgG absorption was lower (P < 0.001) in the progeny of ewes who received supplementary minerals (W-6, 0.069, W-4, 0.078, W-2, 0.072, W-0, 0.261; s.e. 0.0244. P < 0.001) regardless of the duration of the mineral/vitamin supplementation period and this resulted in a reduced concentration of IgG in the lamb's serum. In experiment 2, 40 twin-bearing ewes were allocated to one of four dietary treatments (no. = 10) and offered a basal diet of grass silage ad libitum which was supplemented initially with 500 g of a concentrate containing 140 g crude protein (CP) per kg from day 98 to 133 of gestation and then replaced with 700 g/day of a concentrate containing 180 g/kg CP from day 134 of gestation until lambing, in addition to one of the following mineral/vitamin supplementation treatments : no supplementary minerals, W0 (control); 48 g of supplement per ewe per day in weeks 6 and 5 pre- partum (W6–5), or weeks 4 and 3 pre-partum (W4–3), or for the final 2 weeks pre-partum (W2–1). The ewes were milked and the lambs fed as in experiment 1. Again, treatment had no effect (P > 0.05) on the yields of colostrum or IgG to 18 h post partum. When ewes were offered the mineral/vitamin supplement in the final 2 weeks of gestation their progeny had a lower (P < 0.01) serum IgG concentration (4.6 g/l) than in the control treatment (14.0 g/l) or when the supplement was offered either in weeks 3 and 4 (11.3 g/l) or weeks 5 and 6 pre-partum (14.3 g/l). IgG absorption efficiency followed the same pattern as lamb serum IgG concentration. We conclude that supplementation of the ewe's diet at the level used in these studies for the final 2 weeks of pregnancy results in the production of offspring with a reduced ability to absorb colostral IgG. Furthermore, in order for this impairment of the IgG absorptive ability of the lamb to manifest itself the supplementation must occur for the final 2 weeks of gestation and supplementation for a 2-weekly period earlier in gestation will not elicit the same effect.

The effect of site of starch digestion on glucose metabolism in dairy cows was studied. Four multiparous Israeli-Holstein cows in mid lactation were used in a 4 × 4 Latin-square design. Average body weight of cows was 580 ± 38 kg, and average milk yield was 28 ± 3 kg/day. The cows were fitted with ruminal cannula and flexible T-cannulae in abomasum and ileum. Treatments were as follows : CON (control) : water was infused to the rumen. SR (starch-rumen) : 1.5 kg/day of maize starch solution was infused into the rumen. SA (starch-abomasum) : 1.5 kg/day of maize starch solution was infused into the abomasum. SCA (starch-casein-abomasum) : 500 g/day sodium caseinate and 1.5 kg/day of maize starch solution was infused into the abomasum. Total intake of dry matter (DM), was similar in all treatments and averaged 19.9 kg/day. Total non-structural carbohydrate (TNC) intake averaged in 6.8 kg/day. The average TNC digested in the rumen was 4.95 kg/day for CON and SR cows and 3.34 kg/day for the SA and the SCA cows. The average TNC digestion in the small intestine was 1.18 kg/day for CON and SR cows and 2.41 kg/day for the SA and SCA cows. TNC digestibility in the small intestine was highest for the SCA cows at 0.83 as compared with other treatments. Concentrations of plasma glucose and insulin were similar between treatments. No difference between treatments in total volatile fatty acid (VFA) concentration in ruminal fluids was observed. However, propionate proportion in total VFA was higher in the SR cows than in other treatments (P < 0.04). Milk yield and composition were not affected by treatments in the present study. It was concluded that the amount of dietary protein in the small intestine has a considerable effect on TNC digestibility. Under conditions of high milk production and high rumen-by-pass TNC flow, efficiency of TNC utilization might be greater since TNC is digested in the small intestine rather than in the rumen.

Three experiments were carried out to evaluate the effects of varying levels of mineral and iodine supplements when offered to ewes in late pregnancy on lamb serum immunoglobulin G (IgG) concentrations. In experiment 1, 44 individually housed ewes were allocated to one of four treatments (no. = 11) and offered a basal diet of grass silage ad libitum which was supplemented with 500 g/day of a concentrate (190 g/kg of crude protein (CP)), in addition to mineral/vitamin fortification at the rate of 0 g (C), 17.3 g (LM), 34.6 g (MM) or 52.0 g (HM) per day for the final 7 weeks of pregnancy. The mineral/vitamin supplement contained Ca, P, Na, Mg, Mn, Se, I, Co, Mn and vitamin E. The ewes were milked at 1 h, 10 h and 18 h post partum and measured quantities of colostrum, proportional to lamb birth weight, were fed back to the lambs via a stomach tube. Treatment had no effect on total colostrum yield or total IgG yield to 18 h post partum (P > 0.05). There was a linear decrease in serum IgG concentration and IgG absorption efficiency as mineral supplementation increased (P < 0.001). In experiment 2, which was carried out in conjunction with experiment 1, 44 ewes were allocated to four treatments (no. = 11) and offered the same basal silage/concentrate diet as in experiment 1, in addition to receiving one of the following supplements : (C) control, as in experiment 1; (HM), as in experiment 1; (−I), ewes offered the same mineral/vitamin supplement as HM but with iodine excluded; (I0), ewes offered a daily mineral supplement of iodine only at a level of 40 mg per ewe, equivalent to the iodine inclusion in the 52 g of minerals offered in HM. The iodine-supplemented progeny (HM and IO) had lower (P < 0.001) serum IgG concentrations and higher soil scores (P < 0.05) than the C and −I progeny. In experiment 3, the effects of varying levels of iodine supplementation when offered to ewes during the final 6 weeks of pregnancy on lamb serum IgG values were examined. Forty-eight individually housed ewes were allocated to one of four treatments (no. = 12) and offered grass silage ad libitum, which was supplemented initially with 500 g of a concentrate (140 g/kg of CP) from days 99 to 130 of gestation and then replaced with 700 g/day of a concentrate (180 g/kg of CP) from day 131 of gestation until lambing. In addition, the diet of each ewe was supplemented on a daily basis with iodine at the rate of 0 mg (C), 8.9 mg (LI), 17.7 mg (MI) or 26.6 mg (HI). There was a negative linear reduction in serum IgG concentration and IgG absorption efficiency as maternal dietary iodine supplementation increased (P < 0.001). We conclude that supplementation of the ewe's diet in late pregnancy with 17.3 g of a mineral supplement as formulated in the current experiment lowers the lamb's ability to absorb colostral IgG, and offering only the iodine component of this mineral supplement, at a level which approximates to about one third of currently quoted toxicity levels, will result in reduced serum IgG concentration in the lamb. These findings suggest the need to re-examine current toxicity values for iodine.

The lactation cycle of the dairy cow induces large changes in body fat and protein pools, which can be monitored through loin backfat (BF) and longissimus dorsi (LD) measurements. Data from two experiments (exp) using Holstein-Friesian dairy cows (no. = 40 and 32 respectively) were used to study the association of body weight (BW), BF and LD depth with body condition score (BCS) for the last 6 weeks of the dry period (DP) and the first 8 weeks of lactation. Loin and tail BCS were manually assessed (0 to 5 scale) and BF and LD depth were measured by ultrasound at the fifth lumbar process. The BCS data ranged from 1.3 to 3.0 units in the DP, and from about 1.1 to 3.1 units during early lactation in both experiments. Data were analysed by two models: BW, LD or BF = exp + period (DP or lactation) + BCS + interactions + cow + error (model 1); and BCS = exp + period + LD + BF + LD2 + BF2 + exp × LD + exp × BF + exp × LD2 + exp BF2 + period × LD + period × BF + period × LD2 + period × BF2 BF2 + cow + error (model 2).

A first-order autoregressive (AR(1)) covariance structure was employed for the error terms to account for the correlation among repeated measures within cow. Regressions of BW and LD on BCS (model 1) found pre- to post-calving differences (P < 0.001) in intercept for BW and LD, and slope coefficients of 35 (DP) and 21 (lactation) kg BW, and 5.8 mm LD per BCS unit. Regression of BF on BCS (model 1) showed an exp × period interaction (P < 0.001), with 0.4 mm BF (exp 1; P < 0.05) and 2.0 mm BF (exp 2; P < 0.001) per BCS unit. Regression of BCS on LD and BF (model 2) showed intercepts not equal to 0 (P < 0.06), and differences (P < 0.001) between DP and lactation; BCS increased (P < 0.001) by 0.027 units per mm BF and 0.05 units per mm LD, but LD had a quadratic term −0.0004 (P = 0.02). It is concluded that at BCS lower than 3, LD contributes to BCS following a quadratic function, whereas BF causes BCS to increase linearly. Each unit of BCS equated to about 35 and 20 kg BW for DP and lactation periods respectively, to 5.8 mm LD, and to between 0.4 and 2.0 mm BF.

Based on the potential benefits of cis-9, trans-11 conjugated linoleic acid (CLA) for human health there is a need to develop effective strategies for enhancing milk fat CLA concentrations. In this experiment, the effect of forage type and level of concentrate in the diet on milk fatty acid composition was examined in cows given a mixture of fish oil and sunflower oil. Four late lactation Holstein-British Friesian cows were used in a 4 × 4 Latin-square experiment with a 2 × 2 factorial arrangement of treatments and 21-day experimental periods. Treatments consisted of grass (G) or maize (M) silage supplemented with low (L) or high (H) levels of concentrates (65 : 35 and 35 : 65; forage : concentrate ratio, on a dry matter (DM) basis, respectively) offered as a total mixed ration at a restricted level of intake (20 kg DM per day). Lipid supplements (30 g/kg DM) containing fish oil and sunflower oil (2 : 3 w/w) were offered during the last 14 days of each experimental period. Treatments had no effect on total DM intake, milk yield, milk constituent output or milk fat content, but milk protein concentrations were lower (P < 0.05) for G than M diets (mean 43.0 and 47.3 g/kg, respectively). Compared with grass silage, milk fat contained higher (P < 0.05) amounts of C12:0, C14:0, trans C18:1 and long chain ≥ C20 (n-3) polyunsaturated fatty acids (PUFA) and lower (P < 0.05) levels of C18:0 and trans C18:2 when maize silage was offered. Increases in the proportion of concentrate in the diet elevated (P < 0.05) C18:2 (n-6) and long chain ≥ C20 (n-3) PUFA content, but reduced (P < 0.05) the amount of C18:3 (n-3). Concentrations of trans-11 C18:1 in milk were independent of forage type, but tended (P < 0.10) to be lower for high concentrate diets (mean 7.2 and 4.0 g/100 g fatty acids, for L and H respectively). Concentrations of trans-10 C18:1 were higher (P < 0.05) in milk from maize compared with grass silage (mean 10.3 and 4.1 g/100 g fatty acids, respectively) and increased in response to high levels of concentrates in the diet (mean 4.1 and 10.3 g/100 g fatty acids, for L and H, respectively). Forage type had no effect (P > 0.05) on total milk conjugated linoleic acid (CLA) (2.7 and 2.8 g/100 g fatty acids, for M and G, respectively) or cis-9, trans-11 CLA content (2.2 and 2.4 g/100 g fatty acids). Feeding high concentrate diets tended (P < 0.10) to decrease total CLA (3.3 and 2.2 g/100 g fatty acids, for L and H, respectively) and cis-9, trans-11 CLA (2.9 and 1.7 g/100 g fatty acids) concentrations and increase milk trans-9, cis-11 CLA and trans-10, cis-12 CLA content. In conclusion, the basal diet is an important determinant of milk fatty acid composition when a supplement of fish oil and sunflower oil is given.