Nutritional utilization in Malagueña dairy goats differing in genotypes for the content of alphaS1-casein in milk

A study was carried out with 20 goats of the Malagueña breed, half with a high (HG) and half with a low (LG) genetic capability for α_S1-casein (AS1-CN) synthesis, to determine whether the 2 different genotypes (that cause differences in goat milk composition) are related to differences in nutritional feed utilization. Among the 10 HG goats, 7 had BB and 3 had AB genotypes for AS1-CN, whereas there were 7 EF and 3 FF genotypes in the 10 LG goats. The goats were fed diets differing in crude protein content (13.6 vs. 17.7% dry matter for diets 1 and 2, respectively). For each genotype group, a balance trial was conducted with each of the 2 diets in a 2-period balanced changeover designed with half the animals consuming diet 1 and the other half diet 2, determining individual feed intake and the utilization of N and energy in the diets. Greater voluntary feed intake on a metabolic body weight basis among the HG goats was identified as the first possible cause of their milk production. The HG goats also had a greater level of feed utilization, on a metabolic body weight basis, for N and energy intake. Greater ratios of N balance/ digestible N, milk protein N/digestible N, milk energy/ digestible energy, and milk energy/ME were found for HG goats compared with LG. These effects appear to be dependent on the level of protein in the diet, indicating interactive effects. The greater N and energy utilization of HG versus LG goats may explain the differences in milk composition between the 2 genotype groups.     

Effects of diet on casein and fatty acid profiles of milk from goats differing in genotype for αS1-casein synthesis

This study investigated the interactions between nutrition and the genotype at α_S1-CN loci (CSN1S1) in goats, evaluating the impact of fresh forage-based diets and an energy supplement on the casein and fatty acid (FA) profiles of milk from Girgentana goats. Twelve goats were selected for having the same genotype at the α_S2-CN, β-CN, and κ-CN loci and differing in the CSN1S1 genotype: homozygous for strong alleles (AA) or heterozygous for strong and weak alleles (AF). Goats of each genotype were divided into three groups and, according to a 3 × 3 Latin square design, fed ad libitum three diets: sulla fresh forage (SFF), SFF plus 800 g/day of barley (SFB), and mixed hay plus 800 g/day of barley (MHB). The SFB diet led to higher-energy intake and milk yield. The energy-supplemented diets (SFB, MHB) reduced milk fat and urea and increased coagulation time. The fresh forage diets (SFF, SFB) increased dry matter (DM) and crude protein (CP) intake and milk β-CN. Diet had a more pronounced effect than CSN1S1 genotype on milk FA profile, which was healthier from goats fed the SFF diet, due to the higher content of rumenic acid, polyunsaturated, and omega-3 FAs. The AA milk had longer coagulation time and higher curd firmness, higher short- and medium-chain FAs (SMFA), and lower oleic acid than AF milk. Significant diet by genotype interactions indicated the higher milk yield of AA goats than AF goats with the higher-energy SFB diet and the lower synthesis of SMFA in AF than in AA goats with the SFF diet.     

Relation between αS1-casein,genotype, and quality traits of milk from Swedish dairy goats

Locally produced food is becoming popular among Swedish consumers. One product that has increased in popularity is artisan-manufactured goat cheese, and although the dairy goat industry in Sweden is small-scale, production is gradually increasing. In goats, the CSN1S1 gene regulates expression of the protein α_S1-casein (α_S1-CN), which has been found to be important for cheese yield. Over the years, breeding animals have been imported to Sweden from Norway. Historically, a high frequency of the Norwegian goat population carried a polymorphism at the CSN1S1 gene. This polymorphism, called the Norwegian null allele (D), leads to zero or significantly reduced expression of α_S1-CN. Using milk samples from 75 goats, this study investigated associations between expression of α_S1-CN and genotype at the CSN1S1 gene on milk quality traits from Swedish Landrace goats. Milk samples were grouped according to relative level of α_S1-CN (low: 0–6.9% of total protein; medium-high: 7–25% of total protein) and genotype (DD, DG, DA/AG/AA). While the D allele leads to extremely low expression of α_S1-CN, the G allele is low expressing and the A allele is highly expressing for this protein. Principal component analysis was used to explore the total variation in milk quality traits. To evaluate the effect of different allele groups on milk quality attributes, 1-way ANOVA and Tukey pairwise comparison tests were used. The majority (72%) of all goat milk samples investigated showed relative α_S1-CN content of 0% to 6.82% of total protein. The frequency of individuals homozygous for the Norwegian null allele (DD) was 59% in the population of sampled goats, and only 15% carried at least one A allele. A low relative concentration of α_S1-CN was associated with lower total protein, higher pH, and higher relative concentration of β-casein and levels of free fatty acids. Milk from goats homozygous for the null allele (DD) showed a similar pattern as milk with low relative concentration of α_S1-CN, but total protein was only numerically lower, and somatic cell count and α_S2-CN were higher than for the other genotypes. The associations between levels of α_S1-CN and the investigated genotype at the CSN1S1 gene indicate a need for a national breeding program for Swedish dairy goats.     

Influence of feed intake and source of dietary carbohydrate on milk yield and composition, nitrogen balance, and plasma constituents of lactating goats

The influence of diet (synchronized or not synchronized for the degradation rate of the carbohydrate and N fractions) and amount of feed offered [2.40 +/- 0.10 or 2.00 +/- 0.10 kg of dry matter (DM)/d] on milk yield and composition, N balance, and some plasma constituents was studied using 32 multiparous dairy goats (100 +/- 16 d in milk) that were fed a mixed diet for 9 wk. Diets were 40% concentrate with rapidly degraded starch and rapidly degraded N or highly digestible fibers and slowly degraded N. Nitrogen balance was determined at wk 4 and 8. Goats that were fed greater amounts of DM had higher yields of milk, fat-corrected milk, and protein, but lower milk fat concentrations during the whole trial. Raw milk yield was higher at wk 4 and from wk 6 to 7 for goats consuming the rapidly degraded diet than for goats fed the slowly degraded diet at a high feed intake. Concentrations of milk fat tended to be greater for goats fed the rapidly degraded diet at wk 5, 7, and 8. At wk 5 and 6, an interaction between feed intake and diet was observed for milk protein concentration. Nitrogen digestibility, milk N, and N balance were increased for goats fed at high intakes. The output of N in urine and the efficiency of N use for milk output was greater, and N balance was lower, for goats fed the rapidly degraded diet. Plasma concentrations of nonesterified fatty acids, beta-hydroxybutyrate, and urea (wk 2 to 6) were lower, and insulin concentrations were transiently increased, for goats fed at high intakes. Goats fed the rapidly degraded diet compared with goats fed the slowly degraded diet had higher plasma concentrations of urea, which may indicate inefficient use of ruminal N.     

Effect of pregnancy and extended lactation on milk production in dairy goats milked once daily

Thirty multiparous Murciano-Granadina dairy goats milked once daily were used to study the lactational effects of an extended 24-mo kidding interval (K24; n = 14) compared with the traditional 12-mo kidding interval (K12; n = 16). Goats were divided into 2 groups at wk 29 of lactation balanced with respect to parity, milk yield, and somatic cell count. Over a period of 92 wk, K12 goats were mated twice, at wk 29 during the first lactation and at wk 79 during the second lactation, whereas K24 goats were mated once, at wk 79 of extended first lactation. The K12 goats were dried off from wk 14 to 21 of pregnancy (wk 43 to 50 of lactation). Milk yield was recorded from wk 2 to 92, and milk composition was studied from wk 29 to 92. Milk fatty acids were analyzed in milk samples taken at wk 39 (wk 10 of pregnancy) and 55 (wk 5 of subsequent lactation), when milk in udder compartments (cisternal and alveolar) was also evaluated. Average milk yield during the first 29 wk was 2.23 ± 0.13 L/d. Pregnancy reduced milk yield in K12 goats from wk 39 to 42 of lactation compared with K24 goats. During the dry period for K12 goats, milk yield of K24 goats averaged 1.53 ± 0.10 L/d. From wk 51 to 79, K12 goats produced 32% more milk than did K24 goats, but their milk contained lower fat and protein than that of K24 goats. No changes were detected for milk lactose and somatic cell count from wk 51 to 79. From wk 80 to 92, differences in milk yield and milk composition between groups were not significant. Milk of pregnant K12 goats contained higher C_16:1 and conjugated C_18:2 fatty acids, and had a higher desaturase index than milk of open K24 goats at wk 39. In the following lactation (wk 55), milk of K12 goats contained higher C_18:2 and C_18:3, and lower C_16:0 fatty acids, resulting in a lower atherogenicity index compared with K24 goats. Cisternal milk at wk 39 was lower for K12 than K24 goats, whereas alveolar milk did not differ. In K12 goats, values of cisternal milk tripled, but alveolar milk only doubled at wk 55 (wk 5 of subsequent lactation) compared with wk 39, indicating the importance of the cistern in accommodating high milk yield in early lactation. Values of cisternal and alveolar milk did not differ between wk 39 and 55 for K24 goats. Fat content was higher for alveolar milk than cisternal milk for K12 goats at wk 55 and for K24 goats at wk 39 and 55. No differences in milk protein or lactose were detected between cisternal and alveolar milk. In conclusion, pregnancy reduced milk yield from wk 10 after conceiving onwards. Extended lactation did not significantly decrease milk yield (−8.2%), but increased milk components that may contribute to cheese yield, and may be a useful strategy for reducing metabolic stress in early lactation and for simplifying herd management in dairy goats.     

Effects of corn feeding reduced-fat distillers grains with or without monensin on nitrogen,phosphorus, and sulfur utilization and excretion in dairy cows

This study investigated effects of high inclusion of reduced-fat corn distillers grains with solubles (RFDG) with or without monensin on utilization and excretion of dietary N, P, and S. The experiment was conducted for 11 wk (2-wk diet adaptation, 9-wk experimental period of data collection) with 36 Holstein cows in a randomized complete block design. Cows were blocked by parity, days in milk, and milk yield and assigned to the following diets: (1) a control diet (CON); (2) CON with RFDG included at 28.8% (dry matter basis) by replacing soybean meal, soyhulls, and supplemental fat and phosphorus (DG); and (3) DG with monensin (Rumensin; Elanco Animal Health, Greenfield, IN) supplemented at a rate of 20 mg/kg of DM offered (DGMon). Contrasts were used to compare CON versus DG and DG versus DGMon. Inclusion of RFDG at 28.8% of dietary DM replacing mainly soybean meal did not change crude protein content (17.6% on a DM basis) but decreased rumen-degradable protein and increased rumen-undegradable protein. In addition, the DG diets increased P (0.48 vs. 0.36%) and S concentrations (0.41 vs. 0.21%; DM basis) compared with the CON diet. As a result, DG versus CON decreased plasma and milk urea N concentrations and urinary N excretion. However, the increase in P concentration when feeding the DG versus CON diet to lactating cows increased P intake, plasma P concentration, and urinary and fecal P excretion without affecting milk P secretion. Intake of S was greater for cows fed the DG versus CON diet, resulting in greater plasma total S and sulfate concentration and urinary and fecal S excretion. However, milk S secretion was not affected by DG compared with CON. Monensin supplementation to the DG diet did not affect N intake, utilization, and excretion except that apparent N digestibility was lower compared with DG. In addition, feeding the DGMon diet did not affect P and S utilization and excretion compared with DG. The study suggests that inclusion of high RFDG in a ration by replacing mainly soybean meal altered N, P, and S utilization and excretion, but monensin supplementation to a high-RFDG diet, overall, had minimal effects on N, P, and S utilization and excretion in lactating dairy cows.     

Effects of varying dietary protein and energy levels on the production of lactating dairy cows

Forty-five multiparous and 18 primiparous Holstein cows were fed three levels of crude protein (CP), each at three levels of neutral detergent fiber (NDF), to identify optimal dietary CP and energy. Cows were blocked by parity and days in milk into seven groups of nine and randomly assigned to an incomplete 9 x 9 Latin square trial with four, 4-wk periods. Diets were formulated from alfalfa and corn silages, high-moisture corn, soybean meal, minerals, and vitamins. Forage was 60% alfalfa and 40% corn silage on all diets; NDF contents of 36, 32, and 28% were obtained by feeding 75, 63, and 50% forage, respectively. Dietary CP contents of 15.1, 16.7, and 18.4% were obtained by replacing high-moisture corn with soybean meal. Production data were from the last 2 wk of each period. Spot fecal and urine samples were collected from 36 cows to estimate N excretion using fecal indigestible acid detergent fiber (ADF) and urinary creatinine as markers. There were no interactions (P > or = 0.08) between dietary CP and NDF for any trait; thus, effects of CP were not confounded by NDF or vice versa. Intake of DM and fat yield were lower on 15.1% CP than at higher CP. There were linear increases in milk urea and urinary N excretion and linear decreases in N efficiency with increasing CP. Increasing CP from 15.1 to 18.4% reduced milk N from 31 to 25% of dietary N, increased urinary N from 23 to 35% of dietary N, and reduced fecal N from 45 to 41% of dietary N. Decreasing NDF gave linear increases in BW gain, yield of milk, protein, true protein, lactose, and SNF, and milk/DM intake and milk N/N intake, and linear decreases in milk urea. However, fat yield was lower on 28% than 32% NDF. Reducing NDF from 36 to 28% increased purine derivative excretion by 19%, suggesting increased microbial protein. Increasing CP by adding soybean meal to diets fed cows averaging 34 kg/d of milk increased intake and fat yield but depressed N efficiency. Increasing dietary energy by reducing forage improved milk yield and efficiency and decreased excretion of environmentally labile urinary N.     

Short communication: Effect of αS1-casein (CSN1S1) and κ-casein (CSN3) genotypes on milk composition in Murciano-Granadina goats

The effects of the caprine α_S1-casein (CSN1S1) polymorphisms on milk quality have been widely demonstrated. However, much less is known about the consequences of the κ-casein (CSN3) genotype on milk composition in goats. Moreover, the occurrence of interactions between CSN3 and CSN1S1 genotypes has not been investigated. In this study, an association analysis between CSN1S1 and CSN3 genotypes and milk quality traits was performed in 89 Murciano-Granadina goats. Total milk yield as well as total protein, fat, solids-not-fat, lactose, α_S1-casein (CSN1S1), and α_S2-casein (CSN1S2) contents were recorded every other month during a whole lactation (316 observations). Data analysis using a linear mixed model for repeated observations revealed no interaction between the CSN1S1 and CSN3 genotypes. With regard to the effect of the CSN3 locus, AB and BB genotypes were significantly associated with higher levels of total casein and protein content compared with the AA CSN3 genotype. In strong contrast with French breeds, the CSN1S1 genotype did not affect protein, casein, and fat concentrations in Murciano-Granadina goats. These results highlight the importance of taking into consideration the CSN3 genotype when performing selection for milk composition in dairy goats.     

Effect of dietary crude protein degradability and corn processing on lactation performance and milk protein composition and stability

The present study aimed to evaluate the effect of crude protein degradability and corn processing on lactation performance, milk protein composition, milk ethanol stability (MES), heat coagulation time (HCT) at 140°C, and the efficiency of N utilization for dairy cows. Twenty Holstein cows with an average of 162 ± 70 d in milk, 666 ± 7 kg of body weight, and 36 ± 7.8 kg/d of milk yield (MY) were distributed in a Latin square design with 5 contemporaneous balanced squares, 4 periods of 21 d, and 4 treatments (factorial arrangement 2 × 2). Treatment factor 1 was corn processing [ground (GC) or steam-flaked corn (SFC)] and factor 2 was crude protein (CP) degradability (high = 10.7% rumen-degradable protein and 5.1% rumen-undegradable protein; low = 9.5% rumen-degradable protein and 6.3% rumen-undegradable protein; dry matter basis). A significant interaction was observed between CP degradability and corn processing on dry matter intake (DMI). When cows were fed GC with low CP degradability, DMI increased by 1.24 kg/d compared with cows fed GC with high CP degradability; however, CP degradability did not change DMI when cows were fed SFC. Similar interactions were observed for MY, HCT, and lactose content. When cows were fed GC diets, high CP degradability reduced MY by 2.3 kg/d, as well as HCT and lactose content, compared with low CP degradability. However, no effect of CP degradability was observed on those variables when cows were fed SFC diets. The SFC diets increased dry matter and starch total-tract digestibility and reduced β-casein (CN) content (% total milk protein) compared with GC diets. Cows fed low-CP degradability diets had higher glycosylated κ-CN content (% total κ-CN) and MES, as well as milk protein content, 3.5% fat-corrected milk, and efficiency of N for milk production, than cows fed high-CP degradability diets. Therefore, GC and high-CP degradability diets reduced milk production and protein stability. Overall, low CP degradability increased the efficiency of dietary N utilization and MES, probably due to changes in casein micelle composition, as CP degradability or corn processing did not change the milk concentration of ionic calcium. The GC diets increased β-CN content, which could contribute to reducing HTC when cows were fed GC and high-CP degradability diets.     

Newly identified mutations at the CSN1S1 gene in Ethiopian goats affect casein content and coagulation properties of their milk

Very high casein content and good coagulation properties previously observed in some Ethiopian goat breeds led to investigating the α_s1-casein (CSN1S1) gene in these breeds. Selected regions of the CSN1S1 gene were sequenced in 115 goats from 5 breeds (2 indigenous: Arsi-Bale and Somali, 1 exotic: Boer, and 2 crossbreeds: Boer × Arsi-Bale and Boer × Somali). The DNA analysis resulted in 35 new mutations: 3 in exons, 3 in the 5′ untranslated region (UTR), and 29 in the introns. The mutations in exons that resulted in an amino acid shift were then picked to evaluate their influence on individual casein content (α_s1-, α_s2-, β-, and κ-CN), micellar size, and coagulation properties in the milk from the 5 goat breeds. A mutation at nucleotide 10657 (exon 10) involved a transversion: CAG→CCG, resulting in an amino acid exchange Gln₇₇→Pro_77. This mutation was associated with the indigenous breeds only. Two new mutations, at nucleotide 6072 (exon 4) and 12165 (exon 12), revealed synonymous transitions: GTC→GTT in Val₁₅ and AGA→AGG in Arg₁₀₀ of the mature protein. Transitions G→A and C→T at nucleotides 1374 and 1866, respectively, occurred in the 5′ UTR, whereas the third mutation involved a transversion T→G at nucleotide location 1592. The goats were grouped into homozygote new (CC), homozygote reference (AA), and heterozygote (CA) based on the nucleotide that involved the transversion. The content of α_s1-CN (15.32 g/kg) in milk samples of goats homozygous (CC) for this newly identified mutation, Gln₇₇→Pro₇₇ was significantly higher than in milks of heterozygous (CA; 9.05 g/kg) and reference (AA; 7.61 g/kg) genotype animals. The α_s2-, β-, and κ-CN contents showed a similar pattern. Milk from goats with a homozygous new mutation had significantly lower micellar size. Milk from both homozygote and heterozygote new-mutation goats had significantly shorter coagulation rate and stronger gel than the reference genotype. Except the transversion, the sequence corresponded to allele A and presumably derived from it. Therefore, this allele is denoted by A₃. All goats from the reference genotype (AA) were homozygous for the allele at nucleotide position 1374 and 1866, whereas all mutations in the 5′ UTR existed in a heterozygous form in both heterozygous (CA) and the new mutation (CC) genotype. The newly identified mutation (CC) detected in some of the goat breeds is, therefore, important in selection for genetic improvement and high-quality milk for the emerging goat cheese-producing industries. The finding will also benefit farmers raising these goat breeds due to the increased selling price of goats. Further studies should investigate the effect of this amino acid exchange on the secondary and tertiary structure of the α_s1-CN molecule and on the susceptibility of peptide hydrolysis by digestive enzymes.     

Effects of dietary crude protein concentration on late-lactation dairy cow performance and indicators of nitrogen utilization

The objectives of this study were to measure performance responses and to evaluate indictors of N utilization in late-lactation cows fed diets with incremental reductions in crude protein (CP) concentration. Holstein cows (n = 128; 224 ± 54 d in milk) were stratified by parity and days pregnant (86 ± 25 d) and randomly assigned to 1 of 16 pens in a randomized complete block design. For 3 wk, all cows received a covariate diet containing 16.9% CP [dry matter (DM) basis]. For the subsequent 12 wk, pens were randomly assigned to 1 of 4 treatments that contained 16.2, 14.4, 13.1, or 11.8% CP (DM basis). Diets were offered once daily and contained 32.5% corn silage, 32.5% alfalfa silage, 13.5% high-moisture corn, and 21.5% concentrate mix. A reduction in dietary CP was achieved by replacing soybean meal with soy hulls in the concentrate mix (DM basis). Dry matter intake, milk urea N (MUN; mg/dL), and the yield of milk urea N (g/d) decreased linearly with dietary CP. Compared with a 16.2% CP diet, a 14.4% CP diet did not alter milk yield throughout the study, but the 13.1 and 11.8% CP diets reduced milk yield after 4 and 1 wk, respectively. Furthermore, milk protein percentage was reduced for all dietary CP less than 16.2%, but this negative effect was temporary and disappeared after 7 wk for the 14.4% CP diet. In contrast, MUN adjusted to a new steady state within 1 wk for all dietary treatments. Modeling quadratic responses with a plateau led to predictions of no reduction in fat- and protein-corrected milk (32.6 kg/d) and yields of fat (1.31 kg/d), lactose (1.49 kg/d), and true protein (1.12 kg/d) until dietary CP decreased below 15.5, 15.3, 15.9, and 16.2%, respectively. In this study, MUN and the yield of MUN were highly correlated with N intake, milk protein yield, and fat- and protein-corrected milk. Surprisingly, N use efficiency (milk protein N/intake N) was not correlated with any variables related to N utilization and reached an apparent upper limit of approximately 30%. Although this observation may be associated with feeding diets deficient in metabolizable protein, late-lactation cows in this study adjusted to low dietary CP concentration better than anticipated as milk production was 2.6, 3.6, 6.4, and 8.0 kg/d higher than National Research Council (2001)-predicted metabolizable protein-allowable milk for dietary CP of 16.2, 14.4, 13.1, and 11.8%, respectively.     

Effects of flaxseed on protein requirements and N excretion of dairy cows fed diets with two protein concentrations

Thirty-eight midlactating Holstein cows averaging 597 kg of body weight (SD = 59) were used to determine the effects of dietary flaxseed on protein requirement and N excretion in urine and feces. Milk yield and composition, intake, and digestibility were also determined. Cows were allotted from wk 20 to 30 of lactation to 1 of 4 TMR containing 1) no flaxseed (control) and 16% protein (MPC), 2) whole flaxseed and 16% protein (MPF), 3) no flaxseed (control) and 18% protein (HPC), and 4) whole flaxseed and 18% protein (HPF). Cows fed high protein diets had greater feed intake than those fed medium protein diets (20.2 vs. 18.4 kg/d), and cows fed no flaxseed had greater dry matter intake than those fed flaxseed (20.1 vs. 18.5 kg/d). Milk yield was lower for cows fed MPF (20.3 kg/d) than for those fed HPC (24.4 kg/d), HPF (24.9 kg/d), or MPC (24.0 kg/d). Milk protein and lactose concentrations were similar for cows fed MPC and HPC, but flaxseed decreased milk protein concentration in cows fed MPF or HPF compared with cows fed the control diets. Milk fat concentration was similar in cows fed diets with or without flaxseed, but it was decreased by higher protein concentration. Digestibility was generally reduced when diets contained flaxseed and lower protein concentration. Dietary protein had no effect while dietary flaxseed increased fecal N excretion. Retention of N was lower in cows fed flaxseed compared with cows fed the control diets. Feeding flaxseed decreased milk concentrations of short- and medium-chain fatty acids and increased those of long-chain fatty acids. Flaxseed had no effect on the dietary requirement of N by midlactating dairy cows.     

Effects of dietary calcium, vitamin D3, and corn supplementation on growth performance and mineral metabolism in young goats fed whole milk diets

Twenty-four male goats, approximately 2 to 4 wk of age, were allotted to four dietary treatments in a 2 X 2 factorial design and were fed a basal milk diet at 12.5% body weight for 20 wk. Vitamin D3 was added to the milk in two different amounts with and without supplemental CaCO3. At the end of wk 7, corn was added to all diets at 1% body weight. Over 20 wk, average daily gain was unaltered by addition of Ca or vitamin D3 to the diet. When corn was added to the diet, gains increased from 48 to 180 g/d. Plasma Ca concentrations were not affected by dietary treatment. Supplemental Ca decreased plasma Mg concentrations. Corn supplementation curtailed a depression in plasma Mg and seemed to prevent a whole milk-induced hypomagnesemia. Fecal excretion of all minerals measured was increased in goats fed supplemental Ca. Dietary Ca increased urinary Ca but decreased urinary Mg. Percentage of apparent absorption of Ca, Mg, and total ash was lower in Ca-supplemented goats, as was apparent retention of Ca and Mg. The physiological responses reported suggest the goat as a potential research model for mineral metabolism studies in other ruminants.     

Effect on Production of Replacing Dietary Starch with Sucrose in Lactating Dairy Cows

Replacing dietary starch with sugar has been reported to improve production in dairy cows. Two sets of 24 Holstein cows averaging 41 kg/d of milk were fed a covariate diet, blocked by days in milk, and randomly assigned in 2 phases to 4 groups of 6 cows each. Cows were fed experimental diets containing [dry matter (DM) basis]: 39% alfalfa silage, 21% corn silage, 21% rolled high-moisture shelled corn, 9% soybean meal, 2% fat, 1% vitamin-mineral supplement, 7.5% supplemental nonstructural carbohydrate, 16.7% crude protein, and 30% neutral detergent fiber. Nonstructural carbohydrates added to the 4 diets were 1) 7.5% corn starch, 0% sucrose; 2) 5.0% starch, 2.5% sucrose; 3) 2.5% starch, 5.0% sucrose; or 4) 0% starch, 7.5% sucrose. Cows were fed the experimental diets for 8 wk. There were linear increases in DM intake and milk fat content and yield, and linear decreases in ruminal concentrations of ammonia and branched-chain volatile fatty acids, and urinary excretion of urea-N and total N, and urinary urea-N as a proportion of total N, as sucrose replaced corn starch in the diet. Despite these changes, there was no effect of diet on microbial protein formation, estimated from total purine flow at the omasum or purine derivative excretion in the urine, and there were linear decreases in both milk/DM intake and milk N/N-intake when sucrose replaced dietary starch. However, expressing efficiency as fat-corrected milk/DM intake or solids-corrected milk/DM intake indicated that there was no effect of sucrose addition on nutrient utilization. Replacing dietary starch with sucrose increased fat secretion, apparently via increased energy supply because of greater intake. Positive responses normally correlated with improved ruminal N efficiency that were altered by sucrose feeding were not associated with increased protein secretion in this trial.     

Effect of amount and source of dietary nitrogen on milk fat depression in early lactation dairy cows

Twenty-four multiparous and 15 primiparous Holstein cows were fed a total mixed corn silage diet with one of three dietary treatments: 14% crude protein, 22% crude protein (all preformed), or 22% crude protein (preformed plus nonprotein N). Eight multiparous and 5 primiparous cows were randomly assigned to each treatment at calving. The diet contained 23% ADF during wk 1 to 4 postpartum and was lowered to 11% ADF for wk 5 to 12 postpartum. Treatment had no effect on the magnitude of depression in milk fat percentage or milk fat yield in multiparous cows. After fiber was lowered, changes in rumen acetate to propionate ratio, blood glucose, free fatty acids, and insulin were not influenced by treatment. Depression in milk fat percentage for primiparous cows was 19.7, 9.2, and 14.9% for low protein, high protein, and high protein with nonprotein N, respectively. When changed from high fiber to low fiber, the primiparous cows increased milk fat yield 9% for high preformed protein treatment but decreased fat yield for other treatments. Depression in acetate to propionate ratio and increase in blood glucose was least for the high preformed protein group.     

Proteolytic specificity of Lactobacillus delbrueckli subsp. bulgaricus influences functional properties of mozzarella cheese

Low-moisture part-skim Mozzarella cheeses were manufactured from 2% fat milk and aged for 21 d. Treatments included cheeses made with one of three different strains of Lactobacillus delbrueckii ssp. bulgaricus in combination with a single strain of Streptococcus thermophilus. A fourth, control treatment consisted of cheeses made with only S. thermophilus. Although total proteolytic ability of these strains, as indicated by the o-phthaldialdehyde analysis, was similar in each of the three strains of L. bulgaricus, these strains exhibited different proteolytic specificities toward the peptide, alpha(s1)-CN (f 1-23). On the basis of their alpha(s1)-CN (f 1-23) cleavage patterns and a previously described classification, these strains were assigned to the groups I, III, and V. The objective of this study was to investigate the influence of lactobacilli proteolytic systems, based on specificity toward alpha(s1)-CN (f 1-23), on functionality of part-skim Mozzarella cheese. Moisture, fat, protein, salt-in-moisture, and moisture in nonfat substances content of cheeses made with groups I, III, and V strain were similar. Control cheese had a lower moisture content than did other treatments. Significant differences were observed in functional properties between cheeses manufactured using groups III and V strains. Cheeses made with groups I and III strains were similar in their meltability, hardness, cohesiveness, melt strength, and stretch quality. Meltability and cohesiveness increased with age, while melt strength and stretch quality decreased with age for all cheeses. Additionally, HPLC showed that total peak areas of water-soluble peptides derived from cleavage of alpha(s1)-CN (f 1-23) by different strains of lactobacilli could be highly correlated to meltability and stretch characteristics of cheeses made with those strains.     

Milk production and composition in cows and goats fed alpha-ketoisocaproate

To examine whether alpha-ketoisocaproate supplementation affects milk production, 10 goats were fed either 0 or 1.1% calcium-alpha-ketoisocaproate for 2 wk and 12 cows were fed either 0 or .75% Na alpha-ketoisocaproate for 3 wk. Supplementation with alpha-ketoisocaproate increased milk fat content, milk fat yield, and 4% FCM yield in cows by an average of 5, 10, and 8%, respectively, for the treatment period. In cows, response of milk fat yield to alpha-ketoisocaproate was 120 g during wk 1 of treatment but diminished to 55 g by wk 3. Milk yield and milk protein yield tended to be greater in cows fed alpha-ketoisocaproate, but milk production efficiency and body weight were not altered by treatment in either species. Supplementation with alpha-ketoisocaproate had no significant effect on fatty acid composition of milk but tended to increase the percentage of C10 and C12 fatty acids. In goats, supplementation with alpha-ketoisocaproate had no significant effect on milk production or composition, but trends toward increased milk fat and protein content were observed. Results indicate that alpha-ketoisocaproate acutely stimulates milk fat production in lactating cows and that this effect seems to diminish with time.     

Replacing alfalfa silage with tannin-containing birdsfoot trefoil silage in total mixed rations for lactating dairy cows

Two lactation trials were conducted comparing the feeding value of silages made from birdsfoot trefoil (BFT, Lotus corniculatus L.) that had been selected for low (BFTL), medium (BFTM), and high (BFTH) levels of condensed tannins (CT) to an alfalfa silage (AS) when fed as the principal forage in total mixed rations. Diets also included corn silage, high-moisture shelled corn, soybean meal, soy hulls, and supplemental fat. In trial 1, 32 lactating Holstein cows were blocked by days in milk, assigned to treatment sequences in 8 balanced 4 × 4 Latin squares, and fed 50% dietary dry matter from AS or 1 of 3 BFT silages containing 0.6, 1.2, or 1.7% CT. Diets averaged 17.5 to 19.5% crude protein and 26% neutral detergent fiber on a dry matter basis. Data were collected over the last 2 wk of each 4-wk period. Intakes were 1.3 to 2.8 kg of dry matter/d greater on BFT than on AS and cows gained 0.5 kg of body weight/d on BFT diets while losing 0.14 kg of body weight/d on the AS diet; this resulted in greater milk per dry matter intake (DMI) on AS. Linear effects indicated true protein yield and milk urea nitrogen declined with increasing CT concentration and quadratic effects indicated DMI, energy-corrected milk, and fat yield were increased at intermediate CT concentration. True protein yield and apparent N-efficiency were greater, and milk urea nitrogen lower, on all BFT diets than on AS. In trial 2, 50 lactating Holstein cows were fed a covariate AS diet for 2 wk and then blocked by parity and days in milk and randomly assigned to 1 of 5 diets that were fed continuously for 12 wk. Diets contained (dry matter basis) 48% AS, 16% AS plus 32% of 1 of 3 BFT silages with 0.5, 0.8, or 1.5% CT, or 48% of an equal mixture of each BFT silage. Diets averaged 16.5% crude protein and 30% neutral detergent fiber. Intake and milk yield tended to be lower on AS than BFT, but body weight gains averaged 0.6 kg/d on all diets. Cows fed any of the BFT silages had reduced milk urea nitrogen and ruminal ammonia and reduced urinary N excretion. Feeding the BFT mixture reduced concentrations of milk true protein and milk urea nitrogen and depressed apparent nutrient digestibility. Among diets containing the individual BFT silages, linear reductions in DMI and yield of milk, fat, true protein, lactose, and SNF were observed with increasing CT concentration. By contrast, a previous trial with the same BFT populations showed that substituting BFTH silage containing 1.6% CT for AS in rations containing 60% silage dry matter had no effect on intake, increased yield of milk, energy-corrected milk and milk components, elevated protein use-efficiency, but with a more modest reduction in milk urea nitrogen and urinary N excretion. Silage analyses suggested that the inconsistent responses among trials were related to growth environment or ensiling effects that altered tannin-protein interactions in BFT silage. Differences in diet formulation among trials may have also influenced responses. Results from the current and previous trials indicate further work is needed to identify optimum tannin levels in forages.     

Effects of the percentage of concentrate on rumen fermentation, nutrient digestibility, plasma metabolites, and milk composition in mid-lactation goats

The aim of this work was to study the effects of the dietary percentage of concentrate on patterns of intake, the evolution of rumen fermentation characteristics and plasma metabolites after a meal, nutrient digestibility, and milk production and composition in a medium-term trial in dairy goats. These effects have been well studied in dairy cattle but seldom in goats. Thirteen ruminally and duodenally cannulated dairy goats (95 ± 4 d in milk) fed ad libitum were used in this study. Goats were assigned to 1 of 2 dietary treatments: high-concentrate (70% concentrate on dry matter basis) or a low-concentrate (35%) total mixed rations. The experiment was conducted over a period of 10 wk, including 3 wk of adaption to the diets. Patterns of intake, rumen fermentation characteristics, and plasma metabolites after a meal and fatty acids profile of milk fat were compared at the onset and at the end of the experiment. The increase in dietary percentage of concentrate decreased rumen pH, acetate to propionate ratio, ammonia-N concentration, and plasma urea concentration. The percentage of concentrate did not affect total volatile fatty acid concentrations. The high-concentrate diet increased the rate of intake during the morning meal at the onset of the experiment, whereas it decreased total dry matter intake and the rate of intake during the morning meal at the end of the experiment. The high-concentrate diet resulted in greater organic matter digestibility. Raw milk yield and protein yield were greater in goats fed the high-concentrate diet, whereas fat yield was not affected by dietary treatments. The milk fat content was lower in goats fed the high-concentrate diet. Proportions of the trans-C18:1 isomer relative to total fatty acids in milk were higher with the high-concentrate diet, but no modification of the proportion of total trans-C18:1 was detected, in particular no shift from trans-11 C18:1 to trans-10 C18:1 was observed. Further, the isomer trans-10,cis-12 C18:2 was not detected. Data from this study could be used for a new modeling approach or to improve existing models.     

Effect of variation in proportion of cornmeal and steam-rolled corn in diets for dairy cows on behavior, digestion, and yield and composition of milk

Sixty-six lactating multiparous Holstein cows (113+/-46 DIM) housed in a free-stall facility were blocked and assigned randomly to one of three treatments to evaluate the effects on animal performance from feeding cornmeal, cornmeal mixed with steam-rolled corn in a ratio of 1:1 on dry matter basis, or steam-rolled corn. The only difference in the dietary ingredients was the type of corn, which was included in the total mixed ration (TMR) at 17% of dry matter. The densities (g/L) of cornmeal and steam-rolled corn were, respectively, 635 and 553. Diets were fed as TMR and were formulated according to the Cornell Penn Miner Dairy nutrition model. The TMR consisted of 40% forage and 60% concentrate on dry matter basis. The first 2 wk of the 8-wk study was a preliminary period, and data collected during this period were used as covariate in statistical analysis of production data collected during wk 6 to 8. Treatment diets were fed from wk 3 to 8. Total tract digestibilities of dry matter, organic matter, crude protein, starch, and neutral detergent fiber were not significantly different among treatments. Cows fed TMR containing steam-rolled corn had higher body condition and ruminated longer. However, feeding cornmeal and steam-rolled corn together did not improve dry matter and nutrient digestion, milk yield, 3.5% fat-corrected milk yield, and percentage and yield of fat, crude protein, true protein, and lactose in milk, and milk urea nitrogen. In conclusion, feeding steam-rolled corn improved animal body condition and rumination. Partial or complete substitution of cornmeal by steam-rolled corn in diets for lactating dairy cows did not improve dry matter and nutrient digestion, milk yield, and milk composition.