Partial feed restriction decreases growth hormone receptor 1A mRNA expression in postpartum dairy cows

Uncoupling of the growth hormone (GH) axis in early postpartum dairy cows is correlated with a decrease in liver GH receptor (GHR) 1A mRNA and a decrease in liver GH receptor protein. Postpartum recoupling of the GH axis is also correlated with GHR 1A mRNA and GHR protein. We hypothesized that dry matter intake (DMI) partially controls the increase in GHR 1A mRNA postpartum. Prepartum Holstein dairy cows (n = 11) were offered feed ad libitum. After calving, 6 cows were fed 70% of their expected DMI (feed restriction) for 14 d and 5 cows were fed ad libitum (control). Both groups were fed ad libitum after d 14. Liver was biopsied prepartum and on d 1, 7, 14, and 21 postpartum; blood was sampled throughout the experimental period. Rate of increase in postpartum milk production was less for feed-restricted cows. The GHR 1A mRNA decreased from prepartum to d 1 postpartum and subsequently increased. Rate of postpartum increase in GHR 1A mRNA was less in feed-restricted cows. Diminished GHR 1A persisted for at least 7 d after feed-restricted cows returned to ad libitum feeding. Liver insulin-like growth factor-I mRNA concentrations decreased from prepartum to d 1 as well, but were similar for feed restricted and control thereafter. We concluded that DMI partially controls GHR 1A mRNA expression in early postpartum dairy cows and that the decrease in GHR 1A in response to feed restriction persisted for at least 1 wk after ad libitum feeding was restored.     

Metabolic effects of abomasal L-carnitine infusion and feed restriction in lactating Holstein cows

l-Carnitine is required for mitochondrial fatty acid oxidation, but the effects of carnitine supplementation on nutrient metabolism during dry matter intake depression have not been determined in dairy cows. Studies in other species have revealed responses to l-carnitine that may be of specific benefit to dairy cows during the periparturient period. Eight lactating Holstein cows (132 ± 36 d in milk) were used in a replicated 4 × 4 Latin square experiment with 14-d periods. Treatments were factorial combinations of abomasal infusion of either water or l-carnitine (20 g/d; d 5 to 14) and either ad libitum or restricted intake (50% of previous 5-d dry matter intake; d 10 to 14) of a balanced lactation diet. Liver and muscle biopsies were obtained on d 14 of each period. Feed restriction induced negative balances of energy and metabolizable protein. In feed-restricted cows, carnitine infusion increased 3.5% fat-corrected milk yield compared with those infused with water. Total carnitine concentration in liver was increased in feed-restricted cows infused with carnitine but not in feed-restricted cows infused with water. Carnitine infusion stimulated in vitro oxidation of [1-¹⁴C] palmitate to acid-soluble products and decreased the proportion of [1-¹⁴C] palmitate that was converted to esterified products by liver slices. Feed-restricted cows infused with carnitine had lower liver total lipid concentration and tended to have decreased triglyceride accumulation compared with feed-restricted cows infused with water. Plasma nonesterified fatty acid concentration was not altered by carnitine infusion but was increased by feed restriction; serum β-hydroxybutyric acid was increased by carnitine infusion in feed-restricted cows. In cows fed for ad libitum intake, carnitine infusion affected β-hydroxybutyric acid, insulin, and urea N in serum, liver glycogen concentration, and in vitro alanine oxidation by liver slices, suggesting that hepatic and peripheral nutrient metabolism was influenced. l-Carnitine infusion effectively decreased liver lipid accumulation during feed restriction as a result of greater capacity for hepatic fatty acid oxidation. Further research examining dietary supplementation of l-carnitine during the periparturient period is warranted.     

Effect of L-carnitine infusion and feed restriction on carnitine status in lactating Holstein cows

Previously we determined that abomasal infusion of l-carnitine increased in vitro hepatic fatty acid oxidation, decreased liver lipid accumulation, and supported higher fat-corrected milk yield in feed-restricted lactating cows. The objectives of this study were to examine the effects of supplemental l-carni-tine and amount of feed intake on free carnitine and carnitine ester concentrations in liver, muscle, milk, and plasma of lactating dairy cows. Eight lactating Holstein cows (132 ± 36 d in milk) were used in a replicated 4 × 4 Latin square design with 14-d periods to test factorial combinations of water or l-carnitine infusion (20 g/d; d 5 to 14) and ad libitum or restricted (50% of previous 5-d intake; d 10 to 14) dry matter intake. Plasma was obtained 3 times daily on d 4, 8, and 12; milk samples were collected on d 8, 9, 13, and 14. Liver and muscle were biopsied on d 14 of each period. Free carnitine, short-chain acylcarnitine, and long-chain acylcarnitine concentrations were determined using a radioenzymatic assay coupled with ion exchange chromatography. Abomasal l-carnitine infusion increased total carnitine in plasma on d 8 and d 12. All liver carnitine fractions were increased by carnitine infusion. Feed restriction elevated concentrations of free carnitine, long-chain acylcarnitine, and total carnitine in liver tissue from carnitine-infused cows but not in those infused with water. In muscle, acid-soluble carnitine, long-chain acylcarnitine, and total carnitine concentrations were increased by carnitine infusion and feed restriction without significant interaction. Feed restriction increased free carnitine concentrations in muscle from water-infused cows but not in carnitine-infused cows. Carnitine infusion increased the concentration of each milk carnitine fraction as well as milk carnitine output on d 8 to 9. On d 13 to 14, all carnitine fractions except short-chain acylcarnitine were increased in milk from water-infused, feed-restricted cows, whereas all fractions were increased in carnitine-infused, feed-restricted cows. Carnitine infusion increased total carnitine in plasma, liver, muscle, and milk during feed restriction, whereas feed restriction alone increased carnitine concentrations in muscle and milk but not in liver. Liver carnitine concentrations might limit hepatic fatty acid oxidation capacity in dairy cows during the periparturient period; therefore, supplemental l-carnitine might decrease liver lipid accumulation in periparturient cows.     

Dietary restriction improved feed efficiency of inefficient lactating cows

The aim of this study was to reduce voluntary dry matter intake (DMI) to increase feeding efficiency of preclassified inefficient (INE) dairy cows through restricted feeding. We studied the effects of dietary restriction on eating behavior, milk and energy-corrected milk (ECM) production, in vivo digestibility, energy balance, and measures of feed efficiency [residual feed intake (RFI) and ECM/DMI]. Before the experiment, 12 pairs of cows were classified as INE. The 2 dietary treatments consisted of ad libitum feeding versus restricted feeding of the same total mixed ration containing 36.5% roughage. Inefficient cows fed the restricted total mixed ration had a shorter eating time and lower meal and visit frequency, but a similar rate of eating, meal size, and meal duration compared with INE cows fed ad libitum. Compared with the INE cows fed ad libitum, restricted INE cows had 12.8% lower intake, their dry matter and neutral detergent fiber digestibility remained similar, and their ECM yield was 5.3% lower. Feed efficiency, measured as RFI, ECM/DMI, and net energy retained divided by digestible energy intake, was improved in the restricted INE cows as compared with the ad libitum cows. Our results show that moderate DMI restriction has the potential to improve feed efficiency of preclassified INE cows.     

Effects of late-gestation heat stress independent of reduced feed intake on colostrum,metabolism at calving,and milk yield in early lactation of dairy cows

The objective of this study was to differentiate the effects of acute heat stress (HS) from those of decreased dry matter intake (DMI) during the prepartum period on metabolism, colostrum, and subsequent production of dairy cows. Holstein dairy cows (n = 30) with similar parity and body weight were randomly assigned to 1 of 3 treatments on 45 d before calving: (1) cooled (CL, n = 10) conditions with ad libitum feed intake, (2) HS conditions with ad libitum feed intake (n = 10), and (3) pair-fed cooled (CLPF, n = 10) with reduced DMI similar to the HS group while housed under cooled conditions. The reduction in the amount of feed offered to the CLPF cows was calculated daily as the percentage decrease from the average DMI of HS cows relative to the CL cows. For CLPF and CL cows, barns provided shade, sprinklers, and fans, whereas the HS cows were provided only with shade. Cows in all groups received individually the same total mixed ration. Cows were dried off 60 d before the expected calving. Cows in the HS group and, by design, the CLPF cows had reduced DMI (~20%) during the experiment. Heat stress decreased gestation length, first colostrum yield, and calf birth weight compared with CL and CLPF cows. Milk yield decreased 21% (5 kg) in the HS and 8% (2 kg) in CLPF cows, indicating that reduced feed intake during late gestation accounted for 60% of the total reduced milk yield. The CLPF cows exhibited an elevated NEFA concentration compared with the CL and HS cows. The HS cows had a greater mRNA abundance of HSP70 in the peripheral blood leukocytes at 21 d prepartum compared with the other groups. At calving, the mRNA abundance of HSP70 was greater in HS cows, followed by CLPF, compared with the CL cows. In conclusion, HS during the late gestation period caused metabolism and production differences, which were only partially attributed to reduced feed intake in dairy cows.     

Glucose and insulin responses to an intravenous glucose tolerance test administered to feed-restricted dairy cows receiving folic acid and vitamin B12 supplements

The present experiment was conducted to determine whether, during periods of negative energy balance, the increase in glucose availability, despite similar DMI and greater milk production, induced by a combined supplement of folic acid and vitamin B₁₂ was related to effects of insulin on metabolism. Sixteen multiparous Holstein cows averaging 45 days in milk (standard deviation: 3) were assigned to 8 blocks of 2 animals each according to their milk production (45 kg/d; standard deviation: 6) during the week preceding the beginning of the experiment. Within each block, they received weekly intramuscular injections of either saline (CON) or folic acid and vitamin B₁₂ (VIT) during 5 consecutive weeks. During the last week, the cows were fed 75% of their ad libitum intake during 4 d. Blood samples were taken the morning before starting the feed restriction and on the third day of feed restriction. On the fourth day of feed restriction, the daily meal was not served and an intravenous glucose tolerance test was performed. During the 4 wk preceding the feed restriction, milk production and DMI were not affected by treatments. During the feed restriction, the vitamin supplement tended to decrease milk fat concentration and increase milk concentration of lactose. Plasma concentrations of homocysteine, Ile, Leu, Val, and branched-chain AA increased in VIT cows during the restriction but not in CON cows. During the glucose tolerance test, insulin peak height was lower and insulin incremental positive area under the curve tended to be lower for VIT than for CON [83 (95% confidence interval, CI: 64–108) vs. 123 (95% CI: 84–180) µg·180 min/L, respectively]. Free fatty acid nadir was reached earlier for VIT than for CON [34 (95% CI: 26–43) vs. 46 (95% CI: 31–57) min, respectively]. Glucose area under the curve, clearance rate and peak height, insulin time to reach the peak and clearance rate, and free fatty acid nadir did not differ between VIT and CON. The reduction in insulin release during a glucose tolerance test without changes in glucose clearance rate or area under the curve suggests that the vitamin supplement improved insulin sensitivity in feed-restricted lactating dairy cows.     

Limit-feeding a high-energy diet to meet energy requirements in the dry period alters plasma metabolite concentrations but does not affect intake or milk production in early lactation

Limit-feeding dry cows a high-energy diet may enable adequate energy intake to be sustained as parturition approaches, thus reducing the extent of negative energy balance after parturition. Our objective was to evaluate the effect of dry period feeding strategy on plasma concentrations of hormones and metabolites that reflect energy status. Multiparous Holstein cows (n = 18) were dried off 45 d before expected parturition, paired by expected calving date, parity, and previous lactation milk yield, and randomly assigned to 1 of 2 dry-period diets formulated to meet nutrient requirements at ad libitum or limited intakes. All cows were fed the same diet for ad libitum intake after parturition. Prepartum dry matter intake (DMI) for limit-fed cows was 9.4 kg/d vs. 13.7 kg/d for cows fed ad libitum. During the dry period, limit-fed cows consumed enough feed to meet calculated energy requirements, and ad libitum-fed cows were in positive calculated net energy for lactation (NE_L) balance (0.02 vs. 6.37 Mcal/d, respectively). After parturition, milk yield, milk protein concentration, DMI, body condition score, and body weight were not affected by the prepartum treatments. Cows limit fed during the dry period had a less-negative calculated energy balance during wk 1 postpartum. Milk fat concentration and yield were greater for the ad libitum treatment during wk 1 but were lower in wk 2 and 3 postpartum. Plasma insulin and glucose concentrations decreased after calving. Plasma insulin concentration was greater in ad libitum-fed cows on d −2 relative to calving, but did not differ by dietary treatment at other times. Plasma glucose concentrations were lower before and after parturition for cows limit-fed during the dry period. Plasma nonesterified fatty acid concentrations peaked after parturition on d 1 and 4 for the limit-fed and ad libitum treatments, respectively, and were greater for limit-fed cows on d −18, −9, −5, and −2. Plasma tumor necrosis factor-α concentrations did not differ by treatment in either the pre- or postpartum period, but tended to decrease after parturition. Apart from a reduction in body energy loss in the first week after calving, limit feeding a higher NE_L diet during the dry period had little effect on intake and milk production during the first month of lactation.     

Mammary epithelium disruption and mammary epithelial cell exfoliation during milking in dairy cows

The presence of mammary epithelial cells (MEC) in the milk of ruminants indicates that some MEC are shed from the mammary epithelium; however, the mechanisms that regulate the MEC exfoliation process are not known. Through the release of oxytocin, prolactin, and cortisol and through oxytocin-induced mechanical forces on the mammary epithelium, milking could participate in regulating the MEC exfoliation process. The aims of the present study were to determine the rate of MEC exfoliation throughout milking and to investigate its relationship to mammary epithelium integrity and milking-induced hormone release. Milk samples from 9 Holstein dairy cows producing 40.6 ± 1.36 kg of milk/d were collected at the beginning (after 1 and 2 min), in the middle, and at the end of milking. Milk MEC were purified using an immunomagnetic method. Blood samples were collected before, during, and after milking, and the oxytocin, prolactin, and cortisol concentrations in the samples were measured. Tight junction opening was assessed by plasma lactose concentration and the Na⁺:K⁺ ratio in milk. The somatic cell count in milk varied during the course of milking; it decreased at the beginning of milking and then increased, reaching the highest values at the end of milking. Exfoliated MEC were present in all milk samples collected. The presence of MEC in the milk sample collected during min 1 of milking, likely corresponding to the cisternal milk fraction, suggests that MEC were exfoliated between milkings. The observed increase in the Na⁺:K⁺ ratio in milk and in the plasma concentration of lactose indicated that disruption of mammary epithelium integrity occurred during milking. The MEC exfoliation rate at milking was not correlated with the variables describing milking-induced prolactin release but was negatively correlated with cortisol release, suggesting that cortisol may play a role in limiting exfoliation. In conclusion, milking induced a disruption of the mammary epithelial barrier. Mammary epithelial cells may be continuously exfoliated between milkings or exfoliated during milking as a consequence of the oxytocin-induced mechanical forces and the disruption of mammary epithelium integrity.     

Clinical responses to intramammary endotoxin infusion in dairy cows subjected to feed restriction

Nonpregnant, midlactation primiparous Holstein cows were fed ad libitum (n = 12) or at 80% of maintenance energy requirements (n = 12) to determine whether feed restriction influences clinical response to endotoxin-induced mastitis. After 2 wk of ad libitum or restricted feeding, one mammary quarter per cow was infused with 100 microg of endotoxin. Within 3 to 6 h of intramammary infusion, endotoxin increased mean rectal temperature, heart rate, and milk somatic cell count and immunoglobulin (IgG) concentration; and decreased blood leukocyte count and rumen motility in both restricted and ad libitum-fed cows. Mean serum and milk tumor necrosis factor-alpha (TNF-alpha) concentrations showed only modest increases following endotoxin infusion. Restricted fed cows had slightly different acute fever responses and significantly increased heart and respiration rates than ad libitum fed cows. However, feed restriction did not influence mean total leukocyte count, rumen motility, serum TNF-a concentrations or milk IgG and TNF-alpha concentrations. Thus, results of this study suggest that energy balance does not significantly alter clinical symptoms following acute endotoxin-induced mastitis, at least in midlactation cows. As such, negative energy balance may not underlie the increases in severe coliform mastitis commonly observed in periparturient dairy cows.     

Algorithm development for individualized precision feeding of supplemental top dresses to influence feed efficiency of dairy cattle

Individualized, precision feeding of dairy cattle may contribute to profitable and sustainable dairy production. Feeding strategies targeted at optimizing efficiency of individual cows, rather than groups of animals with similar characteristics, is a logical goal of individualized precision feeding. However, algorithms designed to make feeding recommendations for specific animals are scarce. The objective of this study was to develop and test 2 algorithms designed to improve feed efficiency of individual cows by supplementing total mixed rations (TMR) with varying types and amounts of top-dressed feedstuffs. Twenty-four Holstein dairy cows were assigned to 1 of 3 treatment groups as follows: a control group fed a common TMR ad libitum, a group fed individually according to algorithm 1, and a group fed individually according to algorithm 2. Algorithm 1 used a mixed-model approach with feed efficiency as the response variable and automated measurements of production parameters and top-dress type as dependent variables. Cow was treated as a random effect, and cow by top-dress interactions were included if significant. Algorithm 2 grouped cows based on top-dress response efficiency structure using a principal components and k-means clustering. Both algorithms were trained over a 36-d experimental period immediately before testing, and were updated weekly during the 35-d testing period. Production performance responses for dry matter intake (DMI), milk yield, milk fat percentage and yield, milk protein percentage and yield, and feed efficiency were analyzed using a mixed-effects model with fixed effects for feeding algorithm, top dress, week, and the 2- and 3-way interactions among these variables. Milk protein percentage and feed efficiency were significantly affected by the 3-way interaction of top dress, algorithm, and week, and DMI tended to be affected by this 3-way interaction. Feeding algorithm did not affect milk yield, milk fat yield, or milk protein yield. However, feeding costs were reduced, and hence milk revenue increased on the algorithm-fed cows. The efficacy of feeding algorithms differed by top dress and time, and largely relied on DMI shifts to modulate feed efficiency. The net result, for the cumulative feeding groups, was that cows in the algorithm 1 and 2 groups earned over $0.45 and $0.70 more per head per day in comparison to cows on the TMR control, respectively. This study yielded 2 candidate approaches for efficiency-focused, individualized feeding recommendations. Refinement of algorithm selection, development, and training approaches are needed to maximize production parameters through individualized feeding.     

Methane production,rumen fermentation,and diet digestibility of Holstein and Jersey dairy cows being divergent in residual feed intake and fed at 2 forage-to-concentrate ratios

Improving feed efficiency of dairy cows through breeding is expected to reduce enteric methane production per unit of milk produced. This study examined the effect of 2 forage-to-concentrate ratios on methane production, rumen fermentation, and nutrient digestibility in Holstein and Jersey dairy cows divergent in residual feed intake (RFI). Before experimental onset, RFI was estimated using a random regression model on phenotypic herd data. Ten lactating Holstein and 10 lactating Jersey cows were extracted from the herd and allocated to a high or low pre-experimental RFI group of 5 animals each within breed. Cows were fed ad libitum with total mixed rations either low (LC) or high (HC) in concentrates during 3 periods in a crossover design with a back-cross and staggered approach. Forage-to-concentrate ratio was 68:32 for LC and 39:61 for HC. Cows adapted to the diets in 12 to 24 d and feces were subsequently collected on 2 d. Afterward, gas exchange was measured in respiration chambers and rumen liquid was collected once after cows exited the chambers. Pre-experimental RFI was included in the statistical analysis as a class (low and high RFI) or continuous variable. Methane per kilogram of dry matter intake (DMI) was lower for Holsteins than Jerseys and the response to increased concentrate level was more pronounced for Holsteins than Jerseys (27.2 vs.13.8%); a similar pattern was found for the acetate:propionate ratio. However, methane production per kilogram of energy-corrected milk (ECM) was unaffected by breed. Further, total-tract digestibility of neutral detergent fiber was higher for Jerseys than Holsteins. For RFI as a class variable, DMI, methane production regardless of the expression, and digestibility were unaffected by RFI. For RFI as a continuous variable, DMI was lower and methane per kilogram of DMI was higher for cows with negative (efficient) than positive (inefficient) RFI values, and neutral detergent fiber digestibility was higher for Holsteins with negative than positive RFI values, but not for Jerseys. Daily methane production and methane per kilogram of ECM were unaffected by RFI. In conclusion, methane per kilogram of DMI of Jerseys was lowered to a smaller extent in response to the HC diet than of Holsteins. When pre-experimental RFI was used as a continuous variable, higher methane per kilogram of DMI was found for cows with negative RFI than positive RFI values, but not for methane per kilogram of ECM. These findings call for validation in larger studies.     

Feed restriction induces pyruvate carboxylase but not phosphoenolpyruvate carboxykinase in dairy cows

The ability of dairy cattle to adapt to changes in nutrient intake requires appropriately responsive expression of several key genes in liver. Holstein cows were used in 2 experiments to determine the effect of short-term feed restriction on expression of mRNA for gluconeogenic and ureagenic enzymes in liver. In experiment 1, cows were fed a total mixed diet for ad libitum intake for a 5-d period followed by 5 d of 50% of their previous 5-d ad libitum intake followed by 10 d of ad libitum feeding. Liver biopsies and blood samples were obtained on d 5, 10, and 20 of the experiment, the last day of each feeding period. Pyruvate carboxylase (PC) mRNA increased with feed restriction, but phosphoenolpyruvate carboxykinase (PEPCK) was unchanged. Expression of carbamoyl phosphate synthetase (CPS-I), argininosuccinate synthetase, and ornithine transcarbamylase mRNA were not altered by feed restriction; however, CPS-I mRNA expression tended to increase during realimentation. In experiment 2, cows were fed for ad libitum intake for 5 d and then fed 50% of previous intake for 5 d. Liver biopsy samples collected on d 5 and 10 were used for PC mRNA, PEPCK mRNA, and in vitro measure of gluconeogenesis from radiolabelled propionate and lactate. The data indicate expression of genes for key metabolic processes in liver of lactating cows is responsive to feeding level. Expression of PC mRNA is part of the adaptive response to feed intake restriction and is matched by increased capacity for gluconeogenesis from lactate.     

Mammary cell turnover and enzyme activity in dairy cows: effects of milking frequency and diet energy density

The aim of the study was to investigate the effects of diet energy density and milking frequency on mammary cell turnover and synthetic capacity in dairy cows. Experiment 1 used 20 dairy cows. From d 4 to wk 16 postpartum, the cows were fed either a low-energy density or a high-energy density diet. From d 4 through wk 8, half of the cows in each group were milked 3 times (3x) or 2 times (2x) daily. From wk 9 to 16, all cows were milked 2 times daily. Mammary biopsies were obtained at wk 8 and 16 postpartum. In experiment 2, udders of 18 individual cows were milked diagonally 2x and 4x, and biopsies were obtained after 7 d. In experiment 1, cows on the low-energy density diet yielded 17 and 24% less milk during wk 3 to 8 and wk 11 to 16 postpartum, respectively. Furthermore, at 8 wk postpartum, mammary enzyme activities tended to be lower and mammary cell proliferation was lower in cows on the low-energy density diet. Three times daily milking during the first 8 wk postpartum resulted in 11% higher milk yield. Mammary cell turnover or enzyme activities were not significantly affected at 8 wk. The 3x milking for 8 wk resulted only in a transient carryover effect on milk yield and neither cell turnover nor enzyme activities were significantly affected at 16 wk postpartum. In experiment 2, mammary cell turnover and enzyme activity were unaffected after 7 d of 4x milking although milk yield increased by 18%. We conclude that nutrient restriction affects mammary cell turnover and possible enzyme activity, and that tuning of negative feedback loops in response to filling of the gland may be the dominating effects of changes in milking frequency.     

Prepartal plane of nutrition, regardless of dietary energy source, affects periparturient metabolism and dry matter intake in Holstein cows

Previous research in our laboratory showed that dietary fat supplementation during the dry period was associated with decreased peripartum hepatic lipid accumulation. However, fat supplementation decreased dry matter (DM) intake and thereby confounded results. Consequently, 47 Holstein cows with body condition scores (BCS) ≤ 3.5 at dry-off were used to determine whether source or amount of energy fed to dry cows was responsible for the decreased hepatic lipid content. Moderate grain- or fat-supplemented diets [1.50 Mcal of net energy for lactation (NE_L)/kg] were fed from dry-off (60 d before expected parturition) to calving at either ad libitum (160% of NE_L requirement) or restricted (80% of NE_L requirement) intakes. Postpartum, cows were fed a single lactation diet for ad libitum intake and performance was measured for 105 d. Prepartum intakes of DM and NE_L were significantly lower for feed-restricted cows as designed. During the first 21 d postpartum, previously restricted cows had higher intakes of DM and NE_L. Body weights and BCS were lower prepartum for restricted cows but groups converged to similar nadirs postpartum. Restricted-fed cows had lower concentrations of glucose and insulin and increased concentrations of NEFA in plasma during the dry period. Peripartum NEFA rose markedly for all treatments but were higher postpartum for cows previously fed ad libitum. Plasma concentrations of NEFA and BHBA remained lower in cows restricted-during the dry period. Postpartum concentrations of total lipid and triglyceride in liver were lower in cows previously feed-restricted. Across dietary treatments, activity of carnitine palmitoyltransferase (CPT) in hepatic mitochondria was lowest at − 21 d, highest at 1 d, and decreased at 21 and 65 d relative to parturition. The activity of CPT at d 1 tended to be higher for previously feed-restricted cows; thereafter, CPT activity declined more rapidly than in cows fed ad libitum. Nutrient intake during the dry period had more pronounced effects on peripartal lipid metabolism and DMI than did composition of the prepartum diet.     

Amplifying local serotonin signaling prior to dry-off hastens mammary gland involution and redevelopment in dairy cows

The monoamine serotonin (5-hydroxytryptamine, 5-HT) has been reported to inhibit milk protein gene expression and increase mammary epithelial cell (MEC) tight junction permeability after milk stasis. We hypothesized that increasing serotonin synthesis and signaling within the mammary epithelium before milk stasis would increase systemic and local involution markers, and downregulate the expression of milk protein and tight junction during involution, leading to more efficient tissue growth during the redevelopment phase. Herein, we examined the outcomes of increasing local mammary 5-HT synthesis before milk stasis on involution biomarkers, mammary gland microstructure, and gene and protein expression during the dry period. Multiparous Holstein cows were administered intramammary infusions (via the teat canal) of sterile water (CON, 4 mL/teat, n = 7) or 5-hydroxy-l-tryptophan (5-HTP, serotonin precursor, 20 mg/teat, n = 7) once daily for 5 d before dry-off (d 0). Blood, milk, and mammary secretions were collected and analyzed for components and metabolites. Mammary secretions were collected 12 h after the last milking and on d 1 to 4 during the dry period at 1200 h. Mammary gland biopsies were performed on d 4 (i.e., involution phase) and d 36 (i.e., redevelopment phase) of the dry period for histological and molecular evaluation. Milk protein and tight junction gene expression was quantified via real-time PCR. Hematoxylin and eosin staining, immunohistochemistry (Ki67), and immunofluorescence (serotonin, cleaved caspase 3) were performed to visualize tissue microstructure and to quantify serotonin intensity and cell turnover. Data were analyzed in SAS (SAS Institute Inc.) using 2-way ANOVA. After d 0, mammary secretions of 5-HTP cows had increased concentrations of 5-HT, lactoferrin, and bovine serum albumin. On d 1, 5-HTP cows had greater α-lactalbumin concentrations in plasma relative to CON. Serotonin intensity was increased in the mammary tissue of 5-HTP cows on d 4, relative to CON. On d 4, milk protein and tight junction gene expression was downregulated, MEC number was reduced, and cleaved caspase 3 protein was greater in mammary tissue of 5-HTP cows, relative to CON. On d 36, milk protein genes were upregulated, and the lumen:outer alveolar area and Ki67-positive cells were increased in the mammary tissue of 5-HTP cows, relative to CON. Amplifying serotonin signaling in the mammary epithelium before milk stasis at dry-off achieves greater apoptosis, leading to a reduction in MEC, allowing for greater cell proliferation, which results in more MEC during the redevelopment phase preceding the onset of lactation.     

Concentrate supplementation of a diet based on medium-quality grass silage for 4 weeks prepartum: Effects on cow performance,health, metabolic status,and immune function

Because negative energy balance (EB) contributes to transition-period immune dysfunction in dairy cows, dietary management strategies should aim to minimize negative EB during this time. Prepartum diets that oversupply energy may exacerbate negative EB in early lactation, with detrimental effects on immune function. However, with lower body condition score (BCS) cows, it has been shown that offering concentrates in addition to a grass silage-based diet when confined during an 8-wk dry period resulted in increased neutrophil function in early lactation. The aim of this study was to examine if similar benefits occur when concentrate feeding was restricted to a 4-wk period prepartum. Twenty-six multiparous and 22 primiparous Holstein-Friesian cows were offered ad libitum access to medium-quality grass silage until 28 d before their predicted calving dates (actual mean of 32 d prepartum; standard deviation = 6.4). At this time multiparous cows had a mean BCS of 2.9 (standard deviation = 0.12) and primiparous cows a mean BCS of 3.0 (standard deviation = 0.14) on a 1 to 5 scale. Cows were then allocated in a balanced manner to 1 of 2 treatments (13 multiparous cows and 11 primiparous cows on each treatment): silage only (SO) or silage plus concentrates (S+C) until calving. Cows on SO were offered the same grass silage ad libitum. Cows on S+C were offered an ad libitum mixed ration of the same grass silage and additional concentrates in a 60:40 dry matter (DM) ratio, which provided a mean concentrate DM intake (DMI) of 4.5 kg/cow per d. After calving, all cows were offered a common mixed ration (grass silage and concentrates, 40:60 DM ratio) for 70 d postpartum. Offering concentrates in addition to grass silage during the 4 wk prepartum increased prepartum DMI (12.0 versus 10.1 kg/cow per d), EB (+40.0 versus +10.6 MJ/cow per d), and body weight (BW; 640 versus 628 kg), and tended to increase BCS (3.02 versus 2.97). However, postpartum DMI, milk yield, milk composition, BW change, BCS change, serum nonesterified fatty acid, and β-hydroxybutryrate concentrations, health, and corpus luteum measures were unaffected by treatment. The in vitro assays of neutrophil phagocytosis, neutrophil oxidative burst, and interferon gamma production, conducted on blood samples obtained at d 14 prepartum and d 3, 7, 14, and 21 postpartum, were unaffected by treatment. Primiparous cows had higher phagocytic fluorescence intensity at d 14 prepartum and d 3 and 7 postpartum; a higher percentage of neutrophils undergoing oxidative burst at d 3, 7, and 21 postpartum; and a higher oxidative burst fluorescence intensity at d 14 prepartum and d 7, 14, and 21 postpartum compared with multiparous cows. This suggests that neutrophil function of primiparous cows was less sensitive to the changes occurring during the transition period than that of multiparous cows. In conclusion, offering concentrates during the 4-wk period prepartum had no effect on postpartum DMI, milk yield, body tissue mobilization, EB, measures of neutrophil or lymphocyte function, health, or corpus luteum activity.