Higher Milk Protein Content Research Articles

Effect of milk stasis on mammary gland involution and the microRNA profile

The presence of an autocrine factor in milk that can trigger mammary gland involution was proposed more than 50 yr ago. To provide evidence for the existence of one or more autocrine factors, 10 multiparous cows in late lactation were quarter-milked for 7 d. Following this baseline period, the right front quarter of each cow was left unmilked, and the other quarters were milked for 7 d. Before the last milking of that period, milk (mammary secretions) was collected aseptically from both front quarters. After that milking, 250 mL of the collected samples were infused in the cows' respective rear quarters. No quarters were milked for the following 7 d (milk stasis period), and quarter milking was then resumed in all quarters for the last 7 d of the experiment (remilking period). Quarter milk samples were collected during the baseline period, before the milk stasis period, and during the remilking period. These samples were used for measuring milk components and the concentration of involution markers (SCC, BSA, and lactoferrin). Samples of mammary secretions were collected manually from the quarters during the milk stasis period for involution marker determination. We extracted RNA from samples collected from front quarters before the last milking before the milk stasis period for microRNA (miRNA) determination. As anticipated, the longer milk stasis period implemented for the right front quarter resulted in a more advanced involution than in the left front quarter, based on the concentration of involution markers in the mammary secretions, lower milk production recovery, and changes in milk composition during the remilking period. All 3 involution marker concentrations in the mammary secretions increased in both rear quarters, but were greater in the right quarter secretions than in the left quarter secretions. Resuming milking reinitiated milk production in all quarters, but milk production recovery in the right rear quarters was less robust than that in the left rear quarters (54.3 ± 1.4% vs. 61.6 ± 1.4%, respectively). Milk from the quarters infused with mammary secretions (right rear) had a lower lactose content, but a higher milk protein content and higher SCC than the quarters infused with milk. We detected a total of 359 miRNAs, 76 of which were differentially expressed in milk and mammary secretions. Expression of bta-miR-221 and bta-miR-223 was upregulated in mammary secretions 34- and 40-fold, respectively. The results of the present experiment support the contention that milk stasis leads to the accumulation of one or more factors that trigger involution. The results also indicate that milk stasis leads to changes in the miRNA profile of the milk, but whether such changes are a cause or a consequence of the involution process remains to be established.

Nutritional attributes of goat milk obtained from Anglo Nubian, Moxoto, and Saanen breeds in different lactation phases

The chemical composition, protein, and fatty acids profiles in goat milk from Anglo Nubian, Moxoto, and Saanen breeds in different lactation phases were evaluated. Twenty-three goats, after parturition, were randomly selected to be evaluated in 10 periods of 21 days each. Milk production was greatest for Saanen, lower for Anglo Nubian and lowest for Moxoto; milk solids were the inverse. Moxoto goats produced the highest casein content (3.99%, w/v, of milk). Saanen milk had the greatest content of omega-3 and omega-6 fatty acids. The C4:0 and C6:0 fatty acids did not vary between breeds, but C8:0 was greatest for Anglo Nubian, and followed by Saanen and Moxoto. Milk yield was higher for the Saanen breed; however, Anglo Nubian and Moxoto goats may be functionally more suitable for the manufacture of dairy products due to their higher milk protein content, without decrease in solids during lactation.

Exploring the Cholesterol-Modifying Abilities of Lactobacilli Cells in Digestive Models and Dairy Products.

This study aimed to investigate the ability of lactic acid bacteria to remove cholesterol in simulated gastric and intestinal fluids. The findings showed that the amount of cholesterol removed was dependent on the biomass, viability, and bacterial strain. Some cholesterol binding was stable and not released during gastrointestinal transit. The presence of cholesterol affected the fatty acid profile of bacterial cells, potentially influencing their metabolism and functioning. However, adding cholesterol did not significantly impact the survival of lactic acid bacteria during gastrointestinal transit. Storage time, passage, and bacterial culture type did not show significant effects on cholesterol content in fermented dairy products. Variations in cell survival were observed among lactic acid bacteria strains in simulated gastric and intestinal fluids, depending on the environment. Higher milk protein content was found to be more protective for bacterial cells during gastrointestinal transit than fat content. Future research should aim to better understand the impact of cholesterol on lactic acid bacteria metabolism and identify potential health benefits.

Evaluation of milk yield and composition, feed intake, chewing activities, and clinical variables in dairy cows under hot-humid climate of tropical zone

Dairy cows increase heat loads when the temperature-humidity index (THI) value is elevated in the ambient environments. This condition often occurs in the tropical areas due to a higher THI rate throughout seasons. The major objective of the study was to investigate the different responses in milk yield and composition, chewing activities, and health parameters in dairy cows under the dry and wet seasons of tropical climate zone in Indonesia. Twenty mid-lactating Indonesian Holstein-Friesian cows (139.3 ± 24.63 DIM; 10 primiparous and 10 multiparous; 441 ± 21.5 kg BW) were randomly subjected to 2 groups, dairy cows under dry (n = 10) and wet season (n = 10). Both groups received the same diets throughout the experiment. To determine the heat stress condition, the THI values were recorded daily. Overall, a higher number of THI was more pronounced in wet season. A lower dry matter intake (DMI) and milk yield were observed in wet season group. A tendency towards higher milk protein contents was found in dairy cows under dry season compared to cows under wet season. The other milk compositions such as fat, lactose, and SNF remained unchanged in both dry and wet season groups. The comparison between both groups at several time points of eating and ruminating time revealed significantly higher in cows under dry season. Overall, a higher chewing per bolus was observed in cows under dry season than their counterparts. Furthermore, a tendential greater extent rectal temperature pointed in the wet season group compared to the dry season group relatively. Data suggest that a stronger heat stress condition in wet season was more pronounced compared to dry season, with adversely affecting stronger declined DMI, milk yield, and chewing activities of dairy cows.

Effects of essential oils supplementation, associated or not with amylase, on dry matter intake, productive performance, and nitrogen metabolism of dairy cows

The aim was to evaluate the effects of essential oils supplementation, associated or not with amylase, on productive performance, milk fatty acid composition, purine derivatives, ruminal microbial synthesis, and feeding behavior of lactating dairy cows. Thirty-three Holstein dairy cows were blocked by days in milk (78.0 ± 9.51) and allocated according to the milk yield into the treatments: i) no feed additives (CTRL); ii) essential oils (EO), the addition of a blend of essential oils [100 mg/kg dry matter (DM) basis]; and iii) essential oils + amylase (EOam), a combination of essential oils and α-amylase (625 mg/kg DM; provided to achieve 375 KNU/kg of DM). Diets were formulated to requirements supply of 32.0 kg/d and 20.0 kg/d of milk yield and dry matter intake (DMI), respectively, and contained 298 g/kg NDF; 172 g/kg CP, and 282 g/kg starch; DM basis. Cows were adapted to the experimental diets for 14 days and the measurements lasted 56 days. Cows were milked twice daily, and milk samples were collected three times per week in two sequential milkings, to determine fat, protein, lactose, and urea nitrogen contents. The statistical model considered the fixed effects of diet, the week of the measurement period and its interaction, and the random effect of the block. The feed additive supplementation did not affect the DMI (23.9 kg/d). The EOam treatment increased feed efficiency (1.40) compared with CTRL and EO, but there were no differences between CTRL (1.27) and EO (1.21). The inclusion of feed additives did not increase the plasma glucose concentration. EOam increased the milk yield compared to the CTRL (32.2 vs. 28.7 kg/d, respectively). Although, energy-corrected milk (ECM) was not influenced by feed additives. There were no differences for fat (37.4 g/kg), lactose (45.6 g/kg), and milk urea nitrogen contents (17.3 mg/dL). However, cows fed EO had higher milk protein concentration than EOam-fed cows. The use of essential oils associated with amylase increases the milk yield, but not energy-corrected milk yield; it improves the feed efficiency in Holstein dairy cows in mid-lactation, and shifts some ruminal patterns that slightly change the milk fatty acid profile and feeding behavior.

Milk performance and oxidative status responses to rumen protected methionine supplementation in genotyped α-S1 casein lactating dairy goats fed two levels of metabolizable protein diets

In dairy goats, responses to rumen-protected Methionine (RPM) supplementation on milk performance and milk protein synthesis were inconsistent. The objective of the study was to evaluate the effects of supplemental RPM in diets differing in CP content on milk performance, milk composition, plasma concentration of amino-acids (AA) and parameters of oxidative status in goats genotyped for their genetic variant for alpha-S1 casein (CNS1). Sixteen goats (Body weight = 66.6 ± 8.5 kg, days in milk = 89 ± 5) were grouped into 2 blocks (High vs Low) according to their secretion of CNS1 in milk, and within each CNS1 block, goats were selected to make blocks comparable for milk yield, milk protein content, body weight and days in milk. Goats within CNS1 blocks were allotted to 2 periods cross-over (4 wks for each period with one washout week) nested in 2 × 2 factorial design with dietary CP (LP vs HP, 14 vs 16 % CP in TMR fed ad libitum) and RPM supplementation (CTL vs RPM, 0 vs 4 g/d). Dry matter intake and milk yield were individually recorded daily, whereas milk samples for milk composition determination, and blood samples were obtained individually twice weekly, and once weekly, respectively. Blood was sampled for glucose, NEFA, BHB, urea, insulin, total or oxidized glutathion, superoxide dismutase, catalase, malondialdehyde, and protein carbonyl. At the end of each period, blood was sampled during two consecutive wks to determine plasma AA profile. Goats fed HP diet had higher CP, PDIE, and LysDi (lysine digestible in intestine) intake than those fed LP diet, whereas goats supplemented with RPM had higher MetDi (methionine digestible in intestine) intake (P < 0.001) than those fed the CTL diet. Goats fed HP diet had similar milk performance, milk composition and yields, and similar feed, energy and PDI efficiencies, but higher milk urea concentration than those fed LP diet. Goats supplemented with RPM had higher milk yield only when fed the LP diet (RPM x dietary CP: P < 0.02). Compared to goats fed CTL diet, those supplemented with RPM had higher milk protein content, but this was observed only in those fed HP diet (RPM x dietary CP: P < 0.008), especially for Low CNS1 goats (RPM x CNS1: P < 0.05; RPM x dietary CP x CNS1: P < 0.11). Efficiencies of PDI, feed and energy were not altered by RPM supplementation, but CNS1 x dietary CP x RPM interaction was significant for these efficiencies. Goats supplemented with RPM tended to have higher plasma MDA (P < 0.07) and total glutathione concentrations (P < 0.09). In conclusion, increasing dietary CP failed to improve DMI, milk performance, milk protein content and protein yield, which suggest that Net Energy for lactation was a limiting factor of our experimental diets. With RPM supplementation, increase in milk production in the low CP group, and increase in milk protein content in the high CP group suggests that changes in metabolic partition of nutrients between milk secretion vs milk protein synthesis occurs according to the level of limitation of methionine in diet, which may affect the methionine requirement for goat milk production.

Rumen bacteria influence milk protein yield of yak grazing on the Qinghai-Tibet plateau.

ObjectiveRuminants are completely dependent on their microbiota for rumen fermentation, feed digestion, and consequently, their metabolism for productivity. This study aimed to evaluate the rumen bacteria of lactating yaks with different milk protein yields, using high-throughput sequencing technology, in order to understand the influence of these bacteria on milk production.MethodsYaks with similar high milk protein yield (high milk yield and high milk protein content, HH; n = 12) and low milk protein yield (low milk yield and low milk protein content, LL; n = 12) were randomly selected from 57 mid-lactation yaks. Ruminal contents were collected using an oral stomach tube from the 24 yaks selected. High-throughput sequencing of bacterial 16S rRNA gene was used.ResultsRuminal ammonia N, total volatile fatty acids, acetate, propionate, and isobutyrate concentrations were found to be higher in HH than LL yaks. Community richness (Chao 1 index) and diversity indices (Shannon index) of rumen microbiota were higher in LL than HH yaks. Relative abundances of the Bacteroidetes and Tenericutes phyla in the rumen fluid were significantly increased in HH than LL yaks, but significantly decreased for Firmicutes. Relative abundances of the Succiniclasticum, Butyrivibrio 2, Prevotella 1, and Prevotellaceae UCG-001 genera in the rumen fluid of HH yaks was significantly increased, but significantly decreased for Christensenellaceae R-7 group and Coprococcus 1. Principal coordinates analysis on unweighted UniFrac distances revealed that the bacterial community structure of rumen differed between yaks with high and low milk protein yields. Furthermore, rumen microbiota were functionally enriched in relation to transporters, ABC transporters, ribosome, and urine metabolism, and also significantly altered in HH and LL yaks.ConclusionWe observed significant differences in the composition, diversity, fermentation product concentrations, and function of ruminal microorganisms between yaks with high and low milk protein yields, suggesting the potential influence of rumen microbiota on milk protein yield in yaks. A deeper understanding of this process may allow future modulation of the rumen microbiome for improved agricultural yield through bacterial community design.

Candidate Gene of Milk Protein for Genetic Improvement of Dairy Cattle

The objective of this paper is to explore some efforts to increase milk protein of dairy cows through a milk protein control gene selection approach. Improving the quality of cow's milk has shifted to increase milk protein levels, due to nutritional and economic interest. The breeding process in producing dairy cattle with the advantage of having high milk protein content is more effectively carried out by molecular biotechnology approaches. The content of cow's milk protein is controlled by cow's milk protein control genes. In the process to produce dairy cattle with the advantage of having high milk protein content, it can be done with a selection approach based on milk protein control genes, namely CSN1S1, CSN2, CSN1S2, and CSN3. Once known, the main controller gene that causes high levels of cow's milk protein, it will be easy to identify dairy cattle that have these advantages, so that the selection of dairy cattle can be done since at early age.

Field bean inclusion in the diet of early-lactation dairy cows: Effects on performance and nutrient utilization

The European livestock sector has a significant deficit of high-quality protein feed ingredients. Consequently there is interest in using locally grown protein grain crops to partially or completely replace imported protein feeds in dairy cow rations. Field bean (FB; Vicia faba) has been identified as a locally grown crop with significant potential. The current study was designed to examine the effects of FB on cow performance and nutrient utilization in the diet of early-lactation dairy cows, including high levels of FB (up to 8.4 kg/cow per day). The experiment used 72 dairy cows in a 3-treatment continuous design (from calving until wk 20 of lactation). All cows were given ad libitum access to a mixed ration comprising grass silage and concentrates [45:55 on a dry matter (DM) basis]. Concentrates offered contained either 0, 349, or 698 g of FB/kg of concentrate (treatments FB0, FB-Low, and FB-High, respectively), with FB completely replacing soybean meal, rapeseed meal, maize gluten, and wheat in the concentrate for the FB-High treatment. Following completion of the 20-wk experiment, ration digestibility, nutrient utilization, and methane (CH4) production were measured using 4 cows from each treatment. Neither silage DM intake, total DM intake, nor milk yield were affected by treatment. Cows on FB0 had a higher milk fat content than those on FB-High, and cows on FB0 and FB-Low had higher milk protein contents than did those on FB-High. Field bean inclusion increased the degree of saturation of milk fat produced. Milk fat yield, milk protein yield, and milk fat plus protein yield were higher with FB0 than with either FB-Low or FB-High. Treatment had no effect on the digestibility of DM, organic matter, nitrogen (N), gross energy, or neutral detergent fiber, whereas digestibility of acid detergent fiber was higher with FB0 than with FB-High. Neither the efficiency of gross energy or N utilization, nor any of the CH4 production parameters examined, were affected by treatment. Similarly, none of the fertility or health parameters examined were affected by treatment. The reduction in milk fat observed may have been due to the higher starch content of the FB-High diet, and the reduction in milk protein may have been due to a deficit of methionine in the diet. It is likely that these issues could be overcome by changes in ration formulation, thus allowing FB to be included at the higher range without loss in performance.

Increased milk protein content and whey-to-casein ratio in milk served with breakfast cereal reduce postprandial glycemia in healthy adults: An examination of mechanisms of action

This study describes the effects on glycemic response and the underlying mechanisms of action of increasing the protein concentration and decreasing the casein-to-whey ratio in milk when consumed with a high glycemic breakfast cereal. Twelve healthy men and women, aged 18 to 30 yr and with a body mass index of 20 to 24.9 kg/m2, consumed (in random order) milk beverages (250 mL) containing either 3.1 or 9.3% protein and casein-to-whey ratios of either 80:20 or 40:60. We measured postprandial appetite, glucose, regulatory hormones, and stomach emptying rate over 200 min, as well as food intake at an ad libitum meal at 120 min. Although pre-meal appetite was suppressed to a greater extent with milk beverages that had high (9.3%) compared with regular (3.1%) protein content, food intake was similar among all 4 treatments. Pre-meal mean blood glucose was lower with beverages that had high rather than regular milk protein content, with the lowest glucose peaks after the high milk protein treatment with the 40:60 casein-to-whey ratio. Pre-meal insulin and C-peptide levels were not affected by milk protein content or casein-to-whey ratio, but pre-meal glucagon-like peptide 1 was higher after the treatment containing high milk protein and the 40:60 casein-to-whey ratio, and pre-meal cholecystokinin was higher after the treatments containing high milk protein content. Plasma paracetamol response was also lower after the treatments containing high compared with regular milk protein content. When consumed with carbohydrate, milk beverages with high protein content and (to a lesser extent) a decreased casein-to-whey ratio lowered postprandial glycemia through insulin-independent mechanisms, primarily associated with delayed stomach emptying.

Assessment of rumen bacteria in dairy cows with varied milk protein yield

The present study was conducted to assess rumen bacteria in lactating cows with different milk protein yield, aiming to understand the role of rumen bacteria in this trait. Cows with high milk protein yield (high milk yield and high milk protein content, HH; n = 20) and low milk protein yield (low milk yield and low milk protein content, LL; n = 20) were selected from 374 mid-lactation Holstein dairy cows fed a high-grain diet. Measurement of the rumen fermentation products showed that the concentrations of ruminal total volatile fatty acids, propionate, butyrate, and valerate and the proportion of isobutyrate were higher in the HH cows than in the LL cows. Amplicon sequencing analysis of the rumen bacterial community revealed that the richness (Chao 1 index) of rumen microbiota was higher in the LL cows than in the HH cows. Among the 10 predominant bacterial phyla (relative abundance being >0.10%, present in >60% of animals within each group), the relative abundance of Proteobacteria was 1.36-fold higher in the HH cows than in the LL cows. At the genus level, the relative abundance of Succinivibrio was significantly higher and that of Clostridium tended to be higher in the LL cows than in the HH cows. Sharpea was 2.28-fold enriched in the HH cows compared with the LL cows. Different relationships between the relative abundances of rumen microbial taxa and volatile fatty acid concentrations were observed in the HH and the LL animals, respectively. Succinivibrio and Prevotella were positively correlated with acetate, propionate, and valerate in the LL cows, whereas Sharpea was positively correlated with propionate and valerate concentrations in the HH cows. Collectively, our results revealed that rumen bacterial richness and the relative abundances of several bacterial taxa significantly differed between dairy cows with high and low milk protein yields, suggesting the potential roles of rumen microbiota contributing to milk protein yield in dairy cows.

The effects of L-type amino acid transporter 1 on milk protein synthesis in mammary glands of dairy cows

The mammary gland requires the uptake of AA for milk protein synthesis during lactation. The L-type amino acid transporter 1 (LAT1, encoded by SLC7A5), found in many different types of mammalian cells, is indispensable as a transporter of essential AA to maintain cell growth and protein synthesis. However, the function of LAT1 in regulating milk protein synthesis in the mammary gland of the dairy cow remains largely unknown. For the current study, we characterized the relationship between LAT1 expression and milk protein synthesis in lactating dairy cows and investigated whether the mammalian target of rapamycin complex 1 (mTORC1) signaling controls the expression of LAT1 in their mammary glands. We found that LAT1 and the heavy chain of its chaperone, 4F2, were expressed in mammary tissues of lactating cows, with the expression levels of LAT1 and the 4F2 heavy chain being significantly greater in lactating mammary tissues with high-milk protein content (milk yield, 33.8 ± 2.1 kg/d; milk protein concentration >3%, wt/vol,; n = 3) than in tissues from cows with low-milk protein content (milk yield, 33.7 ± 0.5 kg/d; milk protein concentration <3%, wt/vol; n = 3). Immunofluorescence staining of sectioned mammary tissues from cows with high and low milk protein content showed that LAT1 was located on the whole plasma membrane of alveolar epithelial cells, suggesting that LAT1 provides essential AA to the mammary gland. In cultured mammary epithelial cells from the dairy cows with high-milk protein content, knockdown of LAT1 expression decreased cell viability and β-casein expression; in contrast, overexpression of LAT1 had the opposite effect. Inhibition of mTORC1 by rapamycin attenuated the phosphorylation of molecules related to mTORC1 signaling and caused a marked decrease in LAT1 expression in the cultured cells; expression of β-casein also decreased significantly. These results suggest that LAT1 is involved in milk protein synthesis in the mammary glands of lactating dairy cows and that the mTORC1 signaling pathway might be a control point for regulation of LAT1 expression, which could ultimately be used to alter milk protein synthesis.

Ability of dairy cows to be inseminated according to breed and genetic merit for production traits under contrasting pasture-based feeding systems

Strong genetic selection on production traits is considered to be responsible for the declined ability of dairy cows to ensure reproduction. The present study aimed to quantify the effect of genetic characteristics (breeds and genetic merit for production traits) and feeding systems (FS) on the ability of dairy cows to be inseminated. An experiment was conducted during 9 years on Normande and Holstein cows assigned to contrasted pasture-based FS. Diets were based on maize silage in winter and grazing plus concentrate in spring in the High FS; and on grass silage in winter and grazing with no concentrate during spring in the low FS. Within breed, cows were classified into two genetic groups with similar estimated breeding values (EBV) for milk solids: cows with high EBV for milk yield were included in a Milk-Group and those with high EBV for fat and protein contents were included in a Content-Group. Holstein produced more milk throughout lactation than Normande cows (+2294 kg in the High FS and +1280 kg in the Low FS, P<0.001) and lost more body condition to nadir (−1.00 point in the High FS and −0.80 kg in the Low FS, P<0.001). They also showed a poorer ability to be inseminated because of both a delayed commencement of luteal activity (CLA) and delayed first service (more days from start of the breeding season to first service, DAI1). Cows in the Milk-Group produced more milk than cows in the Content-Group, but milk solids production was similar. Cows in the Content-Group had earlier CLA than cows in the Milk-Group (P<0.01). Genetic group neither affected ovulation detection rate nor DAI1. Within breed and FS, cows with high genetic merit for milk yield had later CLA and DAI1. Cows in the High FS produced more milk and lost less condition to nadir than cows in the Low FS. FS did not affect dairy cows’ ability to be inseminated. However, cows with higher milk protein content, and presumably better energy balance, had earlier CLA (P<0.01) and DAI1 (P<0.10). In addition, higher milk yield was associated with poorer ovulation detection rate and oestrus intensity (P<0.05). The study showed that at similar EBV level for milk solids, selection for increased milk fat and protein content resulted in improved cyclicity and similar oestrous expression and submission rates compared with selection for increased milk yield.

Effects of rumen-protected methionine, lysine, and histidine on lactation performance of dairy cows

The objective of this study was to evaluate the effects of supplementing a metabolizable protein (MP)-deficient diet with rumen-protected (RP) Met, Lys, and His, individually or combined, on the performance of lactating dairy cows. The experiment was a 9-wk randomized complete block design with 72 Holstein cows. Following a 2-wk covariate period, cows were blocked by days in milk, milk yield, and parity, and randomly assigned to 1 of the following 6 treatments: (1) MP-adequate diet [MPA; +243g/d MP balance, according to the National Research Council (2001) requirements]; (2) MP-deficient diet (MPD; −54g/d MP balance); (3) MPD supplemented with RPMet (MPDM); (4) MPD supplemented with RPLys (MPDL); (5) MPD supplemented with RPHis (MPDH); and (6) MPD supplemented with RPMet, RPLys, and RPHis (MPDMLH). Dry matter intake (DMI), yields of milk and milk components (fat, protein, lactose) and energy-corrected milk (ECM), feed and ECM feed efficiencies, and milk and plasma urea N were decreased by MPD, compared with MPA. Supplementation of the MPD diet with RPLys increased milk protein content and plasma glucose concentration and tended to increase milk urea N. Addition of RPHis tended to increase DMI, increased milk protein concentration, and numerically increased yields of milk fat, protein, and ECM. In addition to the trends for increased DMI and milk fat content, and higher milk protein concentration, supplementation of the 3 RP AA also increased yields of milk fat, protein, and ECM and ECM feed efficiency. Relative to MPA, milk N efficiency tended to be increased by MPD. Concentrations of plasma essential AA (except Met and Thr) were decreased by MPD compared with MPA. Supplementation of RPMet, RPLys, and RPHis increased plasma Met (except for MPDM), Lys, and His concentrations, respectively. Cows fed MPD had lower blood hemoglobin concentration and numerically higher plasma ghrelin than cows fed MPA. Concentration of total saturated fatty acids in milk fat were or tended to be higher for MPD compared with MPA and MPDMLH, respectively. Concentration of total polyunsaturated and yield of milk odd- and branched-chain fatty acids were or tended to be decreased by MPD compared with MPA. Overall, the results of this study confirm our previous data and suggest that His stimulates DMI and the combination of the 3 RP AA (Met, Lys, and His) has the potential to improve milk and milk component yields in dairy cows fed MP-deficient diets.

Effect of DGAT1 gene variants on milk quantity and quality in Holstein, Simmental and Brown Swiss cattle breeds in Croatia

The aim of this study was to determine allele frequency at the diacylglycerol-O-transferase 1 gene (DGAT1) K232A polymorphic site and effect of allelic variants K and A on milk production traits of Holstein (dairy), Simmental and Brown Swiss (dual purpose) cattle breeds in Croatia. The DNA was extracted from hair of 371 cows, while coding region of DGAT1p.K232A was amplified using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. Dominant frequency of K allele was determined in all three analysed breeds: Holstein (0.775), Simmental (0.616) and Brown Swiss (0.651). The most Holstein cows were homozygotus for KK variant (0.637), while dominant genotype in other two breeds was KA (Simmental 0.647; Brown Swiss 0.644). Positive effect of KK genotype on milk yield was detected in Holstein and Brown Swiss breeds, while in Simmental breed was negative (-220.8 kg; -463.6 kg) in regard to KA and AA genotype. Milk of cows with KK genotype in Holstein breed, KA in Simmental and AA in Brown Swiss were found as the most favourable in terms of fat content. Cows of AA genotype in all the three analysed breeds have had higher milk protein content. Statistical analysis was performed using the GLM procedure, including genotype and breed effects as independent variables. The effects of DGAT1genotypes on milk quantity and quality were not significant (P&gt;0.05).

The effect of milking reinitiation following extended nonmilking periods on lactation in primiparous dairy cows

In dairy cows, extended periods of nonmilking results in reduced milk secretion, modifications in milk composition, and eventually involution of the mammary glands. The aim of this study was to determine the effect of extended nonmilking periods on the recovery of milk yield and composition, and levels of prolactin and insulin-like growth factor-I in pasture-fed cows after resuming milking. Pasture-fed, primiparous, nonpregnant, Friesian dairy cows at mid lactation (mean ± standard deviation, 97±2d in milk, 14.0±2.5 L/d) were divided into 3 groups (n=6 per group). The cows were subjected to nonmilking periods of 7, 14, or 28d. Twice-daily milking was resumed for 7d following the nonmilking periods. Milk yield recoveries at the end of the 7-d remilking period were 91, 51, and 29% for the 7, 14, and 28-d nonmilked groups, respectively. The somatic cell count declined to less than 400,000 cells/mL by d 3 and 6 of remilking for the 7- and 14-d-nonmilked groups, respectively, but remained greater than 800,000 cells/mL in the 28-d-nonmilked group through the 7-d remilking period. By d 7 of remilking, the somatic cell count for the 7-d-nonmilked group was not different from pretrial values. Upon remilking, the milk fat content returned to pretrial values for the 7- and 14-d-nonmilked groups, although it remained lower than pretrial for the 28-d-nonmilked group. All 3 nonmilked groups had a higher milk protein content following 7d of remilking, compared with pretrial values. The lactose content returned to pretrial values for the 7-d-nonmilked group but remained lower for the 14- and 28-d-nonmilked groups. Circulating prolactin concentrations increased once remilking was resumed, compared with the pretrial and nonmilking periods. Prolactin concentrations did not majorly differ between the groups, with the levels upon 7d of remilking remaining higher than the pretrial concentrations and the nonmilked periods. Plasma concentrations of insulin-like growth factor-I increased during the nonmilking period and were greater in all 3 nonmilked groups on d 1 of remilking than pretrial values and returned to pretrial concentrations following remilking for the 7-d-nonmilked group, whereas the 14- and 28-d-nonmilked groups remained higher than the pretrial values. These data indicate that the process of involution is fully reversed after remilking following 7d of milk stasis but more extended periods of nonmilking prevent the complete recovery of lactation. However, even after 28d of milk stasis, the milk synthesis capacity of the mammary gland could still be partially recovered.

Mutations in the MTHFR gene and their associations with milk production traits in dairy goats

It is known that 5,10-methylenetetrahydrofolate reductase (MTHFR) plays a central role in folate metabolism by irreversibly converting 5,10-methylenetetrahydrofolate into 5-methylenetetrahydrofolate, which is the predominant circulating form of folate. Thus, folate is important for milk protein synthesis and it has been suggested that MTHFR may be a key regulator of folate metabolism during milk protein synthesis within mammary epithelial cells. In this study, Xinong Saanen (SN, N=385) and Guanzhong dairy goats (GZ, N=327) were used to detect single nucleotide polymorphisms (SNPs) in the coding regions within the intron–exon boundaries and the proximal flanking regions of the MTHFR gene by DNA sequencing and PCR-restriction fragment length polymorphism. Fourteen polymorphisms were detected in the MTHFR gene of both dairy goat breeds (g.699A>G, g.739C>A, g.995C>T, g.1951C>T, g.1982T>C, g.2115A>G, g.2607G>A, g.2611_2612delCA, g.4800G>A, g.12118T>C, g.12353A>G, g.14064A>G, g.14084A>G, and g.14344A>G). Single SNP-trait association analysis showed that the mutations at the g.1951C>T and g.4800G>A loci had significant effects on the milk protein contents. Thus, the combined genotypes of C25 (TTCCCCGGAA) and C27 (TTTTCCGGGG) can be used for marker-assisted selection to identify individuals with higher milk protein contents in the GZ and SN breeds, respectively. These results extend the spectrum of genetic variation in the caprine MTHFR gene, thereby contributing to goat genetic resources and breeding.

Milk yield and reproductive performance of dairy heifers and cows supplemented with polyunsaturated fatty acids

The objective of this work was to determine productive and fertility responses of Holstein-Friesian heifers and cows to supplementation with extruded linseed and soybean as sources of polyunsaturated fatty acids (PUFAs). Supplementation had a positive effect on profitability, with significant increases in milk yield in supplemented cows, but not in heifers. Treatments had no effect on milk fat content, but higher milk protein contents were observed with supplementation. A higher conception rate was found for supplemented heifers, but not for cows. Fat sources containing PUFAs are recommended for dairy cattle supplementation, since they improve fertility in heifers and milk yield in cows.

Replacing alfalfa silage with corn silage in dairy cow diets: Effects on enteric methane production, ruminal fermentation, digestion, N balance, and milk production

The objective of this study was to determine the effects of replacing alfalfa silage (AS) with corn silage (CS) in dairy cow total mixed rations (TMR) on enteric CH4 emissions, ruminal fermentation characteristics, apparent total-tract digestibility, N balance, and milk production. Nine ruminally cannulated lactating cows were used in a replicated 3×3 Latin square design (32-d period) and fed (ad libitum) a TMR [forage:concentrate ratio of 60:40; dry matter (DM) basis], with the forage portion consisting of either alfalfa silage (0% CS; 56.4% AS in the TMR), a 50:50 mixture of both silages (50% CS; 28.2% AS and 28.2% CS in the TMR), or corn silage (100% CS; 56.4% CS in the TMR). Increasing the CS proportion (i.e., at the expense of AS) in the diet was achieved by decreasing the corn grain proportion and increasing that of soybean meal. Intake of DM and milk yield increased quadratically, whereas DM digestibility increased linearly as the proportion of CS increased in the diet. Increasing the dietary CS proportion resulted in changes (i.e., lower ruminal pH and acetate:propionate ratio, reduced fiber digestibility, decreased protozoa numbers, and lower milk fat and higher milk protein contents) typical of those observed when cows are fed high-starch diets. A quadratic response in daily CH4 emissions was observed in response to increasing the proportion of CS in the diet (440, 483, and 434 g/d for 0% CS, 50% CS, and 100% CS, respectively). Methane production adjusted for intake of DM, and gross or digestible energy was unaffected in cows fed the 50% CS diet, but decreased in cows fed the 100% CS diet (i.e., quadratic effect). Increasing the CS proportion in the diet at the expense of AS improved N utilization, as reflected by the decreases in ruminal NH3 concentration and manure N excretion, suggesting low potential NH3 and N2O emissions. Results from this study, suggest that total replacement of AS with CS in dairy cow diets offers a means of decreasing CH4 output and N losses. However, the reduction in fiber degradation and the resulting increase in volatile solids content of the manure may lead to increased CH4 emissions from manure storage.

Eugenol for dairy cows fed low or high concentrate diets: Effects on digestion, ruminal fermentation characteristics, rumen microbial populations and milk fatty acid profile

Four ruminally cannulated primiparous lactating cows were used in a 4×4 Latin square design experiment (28 d periods) with a 2×2 factorial arrangement of treatments to examine effects of eugenol supplementation, concentrate proportion of the diet and their interaction on digestion, ruminal fermentation, microbial populations, milk production and milk composition, including milk fatty acid (FA) profile. Cows were fed for ad libitum intake a low (LC) or high (HC) concentrate total mixed ration (TMR) without or with eugenol (50mg/kg of dry matter (DM) intake. The forage:concentrate ratio was (DM basis) 650:350 and 350:650 for LC and HC, respectively. Adding eugenol to the diets had no effects on DM intake, digestion, ruminal fermentation, rumen microbial populations of bacteria and protozoa and milk performance. Increasing the concentrate proportion of the diet resulted in changes typical of cows fed high starch diets (i.e., lower ruminal pH and acetate:propionate ratio; shift in bacterial populations; lower milk fat and higher milk protein concentrations). The ratio t-11 18:1 to t-10 18:1 was not affected by dietary treatments, indicating no changes in the pathway of biohydrogenation of FA in the rumen. Despite the alteration of rumen function due to increasing the proportion of the concentrate of the diet, adding eugenol to these high or low concentrate diets did not modify digestion, ruminal fermentation and microbial populations, suggesting that the effect (i.e., antimicrobial) of eugenol is neither pH nor diet dependant. The lack of efficacy of eugenol at the dosage rate evaluated under the experimental conditions of this study suggests that this essential oil may have low potential for use as feed additive in dairy cow nutrition.