Goat's alpha-s1 casein genotype influences its milk fatty acid composition and delta-9 desaturation ratios

Casein SNP in Norwegian goats: additive and dominance effects on milk composition and quality

Background

The four casein proteins in goat milk are encoded by four closely linked casein loci (CSN1S1, CSN2, CSN1S2 and CSN3) within 250 kb on caprine chromosome 6. A deletion in exon 12 of CSN1S1, so far reported only in Norwegian goats, has been found at high frequency (0.73). Such a high frequency is difficult to explain because the national breeding goal selects against the variant's effect.

Methods

In this study, 575 goats were genotyped for 38 Single Nucleotide Polymorphisms (SNP) located within the four casein genes. Milk production records of these goats were obtained from the Norwegian Dairy Goat Control. Test-day mixed models with additive and dominance fixed effects of single SNP were fitted in a model including polygenic effects.

Results

Significant additive effects of single SNP within CSN1S1 and CSN3 were found for fat % and protein %, milk yield and milk taste. The allele with the deletion showed additive and dominance effects on protein % and fat %, and overdominance effects on milk quantity (kg) and lactose %. At its current frequency, the observed dominance (overdominance) effects of the deletion allele reduced its substitution effect (and additive genetic variance available for selection) in the population substantially.

Conclusions

The selection pressure of conventional breeding on the allele with the deletion is limited due to the observed dominance (overdominance) effects. Inclusion of molecular information in the national breeding scheme will reduce the frequency of this deletion in the population.

Effects of partial replacement of concentrate with feed blocks on nutrient utilization, microbial N flow, and milk yield and composition in goats

Two experiments were carried out to evaluate the effect of partial replacement of concentrate with 2 types of feed blocks (FB) on rumen protozoa numbers, nutrient utilization, microbial N flow to the duodenum, and milk yield and composition in goats. The concentrate included oat, corn grain, barley, soybean meal, salt, and vitamin-mineral mixture. The FB (types I and II) were composed of crude 2-stage olive cake (120 or 100g/kg), fava beans (0 or 400g/kg), barley (320 or 200g/kg), beet molasses (220 or 100g/kg), sunflower meal (180 or 0g/kg), quicklime (70 or 90g/kg), salt (60g/kg), urea (0 or 20g/kg), and vitamin-mineral mixture (30g/kg). In experiment 1, 6 adult, dry, nonpregnant, rumen-fistulated Granadina goats (46.9+/-2.15kg of BW) were used and 3 trials were carried out. In each trial, 2 goats were randomly assigned to receive 600g of alfalfa hay and 400g of concentrate (diet AC), 600g of alfalfa hay, 200g of concentrate, and FB I (diet ACBI), or 600g of alfalfa hay, 200g of concentrate, and FB II (diet ACBII) with 6 replications per diet. The FB were supplied ad libitum. The ratio of purine bases to N was higher in solid- and liquid-associated bacteria for FB goats than for AC goats. In experiment 2, 18 Granadina goats (39.6+/-1.89kg of BW) in the middle of the third lactation were used, and 3 trials were carried out by following a 3 x 3 Latin square experimental design. In every trial, 6 animals randomly received 1.0kg of alfalfa hay supplemented with 1.0kg of concentrate (diet AC) or 0.5kg of concentrate and FB I and II (diets ACBI and ACBII) with 18 replications per diet. The FB were supplied ad libitum. The intakes of organic matter and fat were higher with the AC diet than with the FB diets. The intake of acid detergent fiber was higher for FB-containing diets than for the AC diet. The neutral detergent fiber digestibility of FB diets was higher than that of the AC diet. Energy intake was higher for diets AC and ACBII than for ACBI. Microbial N flow was affected by diet. Milk yield was higher in goats fed the AC diet than in those receiving the FB diets. Conjugated linoleic acid content was higher in milk from FB than in milk from AC goats. Our study suggests that FB type II based on local ingredients could be used advantageously to reduce half of the amount of concentrate without detrimental effects on nutrient utilization, N value of the diet, and milk composition. The decrease of milk yield with ACBII compared with that obtained with the AC diet could be compensated by better quality of milk, decreased cost of feeding, and environmental advantage derived of including by-products in FB.

Effect of CSN1S1 genotype and its interaction with diet energy level on milk production and quality in Girgentana goats fed ad libitum

A study was carried out to evaluate how the energy level of the diet can affect milk production and quality in Girgentana lactating goats in relation to polymorphism at the αs1-casein (CSN1S1) genotype locus. Twenty-seven goats, homogeneous for milk production (1·5±0·3 kg/d), days of lactation (90±10 d) and body weight (35·8±5·5 kg) were selected on the basis of their CSN1S1 genotype, as follows: nine goats homozygous for strong (AA) alleles, nine goats homozygous for weak alleles (FF) and nine goats heterozygous (AF). The goats were used in a 3×3 factorial arrangement of treatments, with three genotypes (AA, FF, AF) and three diets at different energy levels (100%, 65% and 30% of hay inclusion). The experiment consisted of three simultaneous 3×3 Latin squares for the three genotypes, with one square for each level of hay inclusion in the diet. All the animals were housed in individual pens. Each experimental period lasted 23 d and consisted of 15 d for adaptation and 8 d for data and sample collection, during which the goats received the scheduled diet ad libitum. The animals were fed three different diets designed to have the same crude protein content (about 15%) but different energy levels: a pelleted alfalfa hay (H100) and two feeds including 65% (H65) and 30% (H30) of alfalfa hay (respectively 1099, 1386 and 1590 kcal NE for lactation/kg DM). All the diets were ground and pelleted (6 mm diameter). AA goats were more productive than AF and FF goats (respectively: 1419v. 1145 and 1014 g/d;P=0·002). Indeed the interaction energy level×genotype was significant (P=0·018): in fact AA goats showed their milk increase only when fed with concentrates. Differences in protein and in casein levels between the three genotypes were in line with results expected from the different allele contribution to αs1-casein synthesis. Milk urea levels were significantly lower in AA goats compared with AF and FF genotypes (respectively 32·7v. 40·4 and 40·4 mg/dl;P=0·049) and significantly lower when goats were fed with 65H and 30H diets than with 100H diet (respectively 37·4 and 34·3v. 41·7 mg/dl;P<0·001). Indeed, a significant interaction genotype×diet (P=0·043) occurred for milk urea, which was significantly lower in AA goats but only when fed with concentrates (65H and 30H). Blood concentrations of energy indicators (glucose, non-esterified fatty acids and beta-hydroxybutyric acid) were not influenced by genotype. The results confirm that strong alleles are associated with a greater efficiency of feed utilization and seem to show that a high energy level of the diet can further improve this efficiency.

Whole intact rapeseeds or sunflower oil in high-forage or high-concentrate diets affects milk yield, milk composition, and mammary gene expression profile in goats

This study aimed to ascertain the response of goat mammary metabolic pathways to concentrate and lipid feeding in relation to milk fatty acid (FA) composition and secretion. Sixteen midlactation multiparous goats received diets differing in forage-to-concentrate ratio [high forage (HF) 64:36, and low forage (LF) 43:57] supplemented or not with lipids [HF with 130 g/d of oil from whole intact rapeseeds (RS) and LF with 130 g/d of sunflower oil (SO)] in a 4 x 4 Latin square design. Milk yield, milk composition, FA profile, and FA secretion were measured, as well as the expression profiles of key genes in mammary metabolism and of 8,382 genes, using a bovine oligonucleotide microarray. After 3 wk of treatment, milk, lactose, and protein yields were lower with HF-RS than with the other diets, whereas treatment had no effect on milk protein content. Milk fat content was higher with the HF-RS and LF-SO diets than with the HF and LF diets, and SO supplementation increased milk fat yield compared with the LF diet. Decreasing the forage-to-concentrate ratio from 64:36 to 43:57 had a limited effect on goat milk FA concentrations and secretions. Supplementing the LF diet with SO changed almost all the FA concentrations, including decreases in medium-chain saturated FA and large increases in trans C18:1 and C18:2 isomers (particularly trans-11 C18:1 and cis-9, trans-11 conjugated linoleic acid), without significant changes in C18:0 and cis-9 C18:1, whereas supplementing the HF diet with RS led to a strong decrease in short- and medium-chain saturated FA and a very strong increase in C18:0 and cis-9 C18:1, without significant changes in trans C18:1 and conjugated linoleic acid. Despite the decreases in milk lactose and protein yields observed with HF-RS, and despite the decrease in milk medium-chain FA and the increase in C18 FA secretion with RS or SO supplementation, none of the dietary treatments had any effect on mammary mRNA expression of the key genes involved in lactose (e.g., alpha-lactalbumin), protein (e.g., beta-casein), and lipid metabolism (e.g., lipoprotein lipase) after 3 wk of treatment. In addition, transcriptome analysis did not provide evidence of treatments inducing significant changes in the expression of specific genes in the mammary gland. However, 2-way hierarchical clustering analysis highlighted different global mammary expression profiles between diets, showing that the gene expression profiles corresponding to the same diet were gathered by common groups of genes. This experiment suggests that after 3 wk of dietary treatment, other factors, such as substrate availability for mammary metabolism, could play an important role in contributing to milk FA responses to changes in diet composition in the goat.

Diet selection and milk production and composition in Girgentana goats with different alpha s1-casein genotype

In goats, alpha s1-casein polymorphism is related to different rates of protein synthesis. Two genetic variants, A and F, have been identified as strong and weak alleles based on a production of 3.5 and 0.45 g/l of alpha s1-casein per allele. The aim of the trial was to test whether goats can select their diet as a function of their genetic aptitude to produce milk at different casein levels and whether this selection can influence milk production or composition. Two groups of 8 animals, homozygous for strong (AA) or weak (FF) alleles were housed in individual pens. Using a manger subdivided into five separate containers, the goats were offered daily for 3 weeks: 1.5 kg of alfalfa pelleted hay, 0.7 kg of whole barley, 0.7 kg of whole maize, 0.7 kg of whole faba bean and 0.7 kg of pelleted sunflower cake. Total dry matter intake was similar between groups and resulted in nutrient inputs much higher than requirements. On average, goats selected 86% of maize plus barley and only 46% of faba bean plus sunflower. Indeed, AA goats selected less faba bean compared with FF goats (37.2 v. 56.7% of the available amount; P=0.01); during week 2 and week 3 they significantly increased maize selection (respectively for week 2 and week 3: 94.9 and 99.1% v. 85.3 and 87.3%) thus increasing the ratio between the high-energy feeds and the high-protein feeds (2.41 v. 1.81, P=0.023). As for true protein, the high soluble fraction (B1) and the indigestible fraction (C) were lower in the diet selected by AA goats (respectively in AA and FF groups: B1, 7.85 v. 9.23% CP, P<0.01; C, 6.07 v. 6.30% CP, P<0.001); these diet characteristics can be associated with lower losses of protein. Milk production, being similar in AA and FF groups when goats were fed with a mixed diet, significantly increased in AA group, when free-choice feeding was given (mean productions: 1198 v. 800 g/d, P<0.01). Casein content was higher in AA group than in FF group (2.70 v. 2.40%, P<0.01) whereas milk urea was higher in FF group (59.7 v. 48.8 mg/dl, P<0.01). In conclusion, when the animals were free to select their diet, their higher genetic aptitude to produce casein seemed to adjust their energy and protein dietary input in qualitative terms, thus leading to an increase in milk production and a decrease in milk urea. These results seem to demonstrate that interactions probably occurred between genetic polymorphism at the alpha s1-casein locus, diet selection and the efficiency of nutrient transformation into milk.

Milk production and composition in Malagueña dairy goats. Effect of genotype for synthesis of αs1-casein on milk production and its interaction with dietary protein content

A study was carried out to analyse the production and composition of milk from Malagueña goats of different genotypes for the content of αs1-casein. Twenty goats were used, half of them with a high (HG) and half with a low (LG) genetic capability for αs1-casein synthesis. Among the ten HG goats, seven had BB and three had AB genotypes, whereas there were seven EF and three FF genotypes among the LG goats. The goats were fed a diet differing in crude protein content, 136 and 177 g/kg dry matter for diet 1 (D1) and diet 2 (D2), respectively. For each genotype group, a trial was conducted, with each of the two diets in a two-period balanced change-over design, in which the milk production and composition were analysed. The genotype was found to determine milk composition, with that produced by the HG goats being higher in total solids, protein, αs1-casein, αs2-casein and fat. Analysis of milk production values and, especially, those of the yields of the different components, revealed an interaction between the factors. HG goats that consumed D1 were more productive than LG goats, but this ceased to be so when the D1 diet was replaced by D2. However, LG goats, although less productive than HG ones when the D1 diet was consumed, showed increased productive capacity when D1 was replaced by D2. The main difference for the fatty acid profile of the dairy fat is that the milk fat produced by the HG goats contained higher levels of short and medium-chain fatty acids. From these results, it is concluded that, in terms of favouring production, the advantage of replacing animals with a low capacity for αs1-casein synthesis with those of a high capacity seems to depend on the protein level in the diet. Similarly, the advantage of changing to a diet of higher protein content depended on the animal's genotype.

Effect of plant oils in the diet on performance and milk fatty acid composition in goats fed diets based on grass hay or maize silage

Based on the potential benefits to long-term human health there is interest in developing sustainable nutritional strategies for reducing saturated and increasing specific unsaturated fatty acids in ruminant milk. The impact of plant oil supplements to diets containing different forages on caprine milk fatty acid composition was examined in two experiments using twenty-seven Alpine goats in replicated 3 x 3 Latin squares with 28 d experimental periods. Treatments comprised of no oil (control) or 130 g/d of sunflower-seed oil (SO) or linseed oil (LO) supplements added to diets based on grass hay (H; experiment 1) or maize silage (M; experiment 2). Milk fat content was enhanced (P<0.01) on HSO, HLO and MLO compared with the corresponding H or M control diets, resulting in 17, 15 and 14% increases in milk fat secretion, respectively. For both experiments, plant oils decreased (P<0.05) milk 10:0-16:0 and odd- and branched-chain fatty acid content and increased 18:0, trans-Delta(6-9,11-14,16)-18:1 (and their corresponding Delta-9 desaturase products), trans-7, trans-9-conjugated linoleic acid (CLA), trans-9, trans-11-CLA and trans-8, cis-10-CLA concentrations. Alterations in the distribution of cis-18:1, trans-18:1, -18:2 and CLA isomers in milk fat were related to plant oil composition and forage in the diet. In conclusion, plant oils represent an effective strategy for altering the fatty acid composition of caprine milk, with evidence that the basal diet is an important determinant of ruminal unsaturated fatty acid metabolism in the goat.

Mammary transcriptome analysis of food-deprived lactating goats highlights genes involved in milk secretion and programmed cell death

Animal nutrition considerably affects milk composition that influences its nutritional quality. Milk component synthesis and secretion by the mammary gland involve expression of a large number of genes whose nutritional regulation remains poorly defined. In this study, we examined the effect of food deprivation (FD) on the expression of 8379 genes in caprine mammary gland using a bovine oligonucleotide microarray. Twelve lactating goats were assigned to 2 groups based on their feeding level (control diet ad libitum vs. 48-h FD). We identified 161 genes whose expression was altered by FD. Most of these genes (88%) were downregulated, suggesting a stress response by the mammary gland. In particular, the decrease in expression of genes involved in milk protein, lactose, and lipid metabolism could contribute together with the shortage of nutrients to the drop in milk protein, lactose, and fat secretion. In addition, this study highlights modification of the expression of at least 14 genes that could be responsible for a slowdown in mammary cell proliferation and differentiation and/or an increase in programmed cell death in response to 48-h FD in goats.