A.G. Rius

Short communication: immediate and deferred milk production responses to concentrate supplements in cows grazing fresh pasture.

The objective of this study was to determine the increase in milk production from supplementation that occurred after supplementation ceased. This portion of the total response (i.e., the deferred response), although accepted, is generally not accounted for in short-term component research projects, but it is important in determining the economic impact of supplementary feeding. Fifty-nine multiparous Holstein-Friesian dairy cows were offered a generous allowance of spring pasture [>45 kg of dry matter (DM)/cow per day) and were supplemented with 0, 3, or 6 kg (DM)/d of pelleted concentrate (half of the allowance at each milking event) in a complete randomized design. Treatments were imposed for the first 12 wk of lactation. Treatments were balanced for cow age (5.4 ± 1.68 yr), calving date (July 27 ± 26.0 d), and genetic merit for milk component yield. During the period of supplementation, milk yield and the yield of milk components increased (1.19 kg of milk, 0.032 kg of fat, 0.048 kg of protein, and 0.058 kg of lactose/kg of concentrate DM consumed), but neither body condition score nor body weight was affected. After concentrate supplementation ceased and cows returned to a common diet of fresh pasture, milk and milk component yields remained greater for 3 wk in the cows previously supplemented. During this 3-wk period, cows that previously received 3 and 6 kg of concentrate DM per day produced an additional 2.3 and 4.5 kg of milk/d, 0.10 and 0.14 kg of fat/d, 0.10 and 0.14 kg of protein/d, and 0.10 and 0.19 kg of lactose/d, respectively, relative to unsupplemented cows. This is equivalent to an additional 0.19 kg of milk, 0.006 kg of fat, 0.006 kg of protein, and 0.008 kg of lactose per 1 kg of concentrate DM previously consumed, which would not be accounted for in the immediate response. As a result of this deferred response to supplements, the total milk production benefit to concentrate supplements is between 7% (lactose yield) and 32% (fat yield) greater than the marginal response measured during the component experiment. Recommendations to dairy producers based on component feeding studies must be revised to include this deferred response.

Once-daily milking during a feed deficit decreases milk production but improves energy status in early lactating grazing dairy cows

The objective of this study was to investigate the effect of milking frequency (MF) at 2 feeding levels (FL) on milk production, body condition score, and metabolic indicators of energy status in grazing dairy cows during early lactation. Multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows (n=120) grazed pasture and were milked twice daily (2×) from calving until 34 ± 6 d in milk (mean ± standard deviation). Cows were then allocated to 1 of 4 treatments in a 2 × 2 factorial arrangement. Treatments consisted of 2 FL: adequately fed [AF; 14.3 kg dry matter intake (DMI)/cow per d] or underfed (UF; 8.3 kg of DMI/cow per d) and 2 MF: 2× or once daily (1×). Treatments were imposed for 3 wk. After the treatment period, all cows were offered a generous pasture allowance (grazing residuals >1,600 kg of dry matter/ha) and milked 2×. During the 3-wk treatment period, we observed an interaction between FL and MF for energy-corrected milk (ECM), such that the decrease due to 1× milking was greater in AF than in UF cows (20 and 14% decrease, respectively). No interactions were found posttreatment. Cows previously UF produced 7% less ECM than AF cows during wk 4 to 12; however, no subsequent effect was observed of the previous underfeeding. Cows previously milked 1× produced 5% less ECM during wk 4 to 12, and differences remained during wk 13 to 23. During the 3-wk treatment period, UF cows lost 0.2 body condition score units (1-10 scale) and this was not affected by 1× milking. During the treatment period, UF cows had lower plasma glucose, insulin, and insulin-like growth factor I, and greater nonesterified fatty acids and β-hydroxybutyrate concentrations than AF cows. Cows milked 1× had greater plasma glucose, insulin, and insulin-like growth factor I, and lower nonesterified fatty acids and β-hydroxybutyrate concentrations compared with cows milked 2×. In conclusion, energy status was improved by 1× milking; however, when UF cows were milked 1×, milk production was reduced by more than underfeeding alone. The immediate and residual responses to 1× milking need to be considered when using this management strategy during a feed deficit.

Temporary alterations to postpartum milking frequency affect whole-lactation milk production and the energy status of pasture-grazed dairy cows

This study investigated the immediate and long-term effects of temporary alterations to postpartum milking frequency (MF) on milk production, body condition score (BCS), and indicators of energy status in pasture-grazed cows supplemented with concentrates. Multiparous Holstein-Friesian cows (n = 150) were randomly assigned to 1 of 5 groups at calving: milked twice daily (2 ×) throughout lactation (control), or milked either once daily (1 ×) or 3 times daily (3 ×) for 3 or 6 wk immediately postpartum, and then 2 × for the remainder of lactation. During wk 1 to 3 postpartum, cows milked 1 × produced 15% less milk and 17% less energy-corrected milk (ECM) than cows milked 2 ×. This immediate production loss increased to 20% less milk and 22% less ECM during wk 4 to 6 postpartum for cows that remained on 1 × milking; these animals also produced less than 1 × cows switched to 2 × milking after 3 wk. During wk 8 to 32, when all cows were milked 2 ×, those previously milked 1 × had sustained reductions in milk (-6%) and ECM (-8%) yields, which were not affected by the duration of reduced postpartum MF. In contrast, cows milked 3 × postpartum had 7% greater milk yields during wk 1 to 6 compared with 2 × controls, irrespective of the duration of increased MF. Milk yields also remained numerically greater (+5%) during wk 8 to 32 in cows previously milked 3 ×. Nevertheless, yields of ECM were not increased by 3 × milking, because of lower milk fat and protein contents that persisted for the rest of lactation. In addition, indicators of cow energy status reflected an increasing state of negative energy balance with increasing MF. Cows milked 1 × postpartum had greater plasma glucose and lower plasma nonesterified fatty acid concentrations during the reduced MF, and plasma glucose remained lower for 2 wk after cows had switched to 2 × milking. Moreover, BCS was improved relative to 2 × controls from wk 5 to 6. In contrast, cows milked 3 × had lower plasma glucose concentrations, greater plasma nonesterified fatty acid concentrations, and greater BCS loss during wk 1 to 3; however, greater body fat mobilization was not sustained, indicating that additional energy supplements may be required to achieve better milk production responses. In conclusion, temporary 1 × milking had lactation-long negative effects on milk and milk component yields but improved cow energy status and BCS, whereas temporary 3 × milking immediately increased milk yield but did not improve milk fat and protein yields in pasture-grazed cows.

Expression of key lipid metabolism genes in adipose tissue is not altered by once-daily milking during a feed restriction of grazing dairy cows.

The objective of this study was to investigate the effect of reduced milking frequency, at 2 feeding levels, on gene expression in adipose tissue of grazing dairy cows during early lactation. Multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows (n=120) were grazed on pasture and milked twice daily (2×) from calving to 34±6d in milk (mean ± standard deviation). Cows were then allocated to 1 of 4 treatments in a 2×2 factorial arrangement. Treatments consisted of 2 milking frequencies (2× or once daily; 1×) and 2 feeding levels for 3 wk: adequately fed (AF), consuming 14.3 kg of dry matter/cow per day, or underfed (UF), consuming 8.3 kg of dry matter/cow per day. After the treatment period, all cows were fed to target grazing residuals ≥1,600 kg of DM/cow per day and milked 2× for 20 wk. Adipose tissue was collected from 12 cows per treatment by subcutaneous biopsy at -1, 3, and 5 wk relative to treatment start, RNA was extracted, and transcript abundance of genes involved in lipid metabolism was quantified using a linear mixed model. At the end of the 3-wk treatment period, transcript abundance of genes involved in fatty acid (FA) uptake into adipose tissue (LPL), FA synthesis [FA synthase (FASN) and stearoyl-coenzyme A desaturase (SCD)], FA oxidation [acyl-coenzyme A synthetase long-chain family member 1 (ACSL1) and carnitine palmitoyltransferase 2 (CPT2)], glyceroneogenesis [glycerol-3-phosphate dehydrogenase 1 (GPD1) and pyruvate carboxylase (PC)], and triacylglyceride synthesis [diacylglycerol O-acyltransferase 2 (DGAT2)] were greater in AF1× cows compared with all other treatments. However, when cows were underfed, no effects of milking frequency were observed on transcript abundance of genes involved in adipose lipid metabolism. Despite increases in plasma NEFA concentrations in UF cows, no effects of underfeeding were observed on the transcription of lipolytic genes. At 5 wk, after cows were returned to 2× milking and standard feed allowance, transcript abundances of genes involved in FA synthesis [acetyl-coenzyme A carboxylase α (ACACA) and SCD)] were increased in cows previously UF. Expression of ACSL1 was decreased in UF1× cows relative to UF2× cows and CPT2 expression was greater in AF1× cows compared with AF2× cows. In conclusion, after 3 wk of reduced milking frequency during a feed restriction, transcription of genes involved in lipid metabolism in adipose tissue were not altered, possibly due to the reduced milk production in these animals. However, 3 wk of 1× milking in AF cows increased transcription of genes involved in FA synthesis, oxidation, and triacylglyceride synthesis.

Lowering rumen-degradable protein maintained energy-corrected milk yield and improved nitrogen-use efficiency in multiparous lactating dairy cows exposed to heat stress

The objective of this study was to examine the effect of reducing rumen-degradable protein (RDP) and rumen-undegradable protein (RUP) proportions on feed intake, milk production, and N-use efficiency in primiparous and multiparous cows exposed to warm climates. Eighteen primiparous and 30 multiparous mid-lactation Holstein cows were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Cows were randomly assigned to 1 of 4 dietary treatments formulated to contain 2 proportions of RDP (10 and 8%) and 2 proportions RUP (8 and 6%) of dry matter (DM) indicated as follows: (1) 10% RDP, 8% RUP; (2) 8% RDP, 8% RUP; (3) 10% RDP, 6% RUP; and (4) 8% RDP, 6% RUP. Protein sources were manipulated to obtain desired RDP and RUP proportions. Diets were isoenergetic and contained 50% forage and 50% concentrate (DM basis). Cows were individually fed the 10% RDP, 8% RUP diet 3 wk before treatment allocation. Cows were exposed to the prevailing Tennessee July and August temperature and humidity in a freestall barn with no supplemental cooling. Main effects and their interaction were tested using the Mixed procedure of SAS (least squares means ± standard error of the mean; SAS Institute Inc., Cary, NC). Observed values of nutrient intake and milk production were used to obtain NRC (2001) model predictions. Cows showed signs of heat stress throughout the study. Reducing from 10 to 8% RDP decreased dry matter intake (DMI; 0.9 kg/d) at 8% RUP, but increased DMI (2.6 kg/d) at 6% RUP in primiparous cows. Reducing from 10 to 8% RDP decreased milk yield (10%) at 8% RUP, but increased yield (14%) at 6% RUP. Treatments did not affect yield of energy-corrected milk. For multiparous cows, treatments did not affect DMI. Reducing from 10 to 8% RDP decreased yield of energy-corrected milk (3.4%) at 8% RUP, but increased yield (8.8%) at 6% RUP. Reducing from 10 to 8% RDP and 8 to 6% RUP both increased N-use efficiency for primiparous and multiparous cows. The NRC model underestimated metabolizable protein and RUP supply, and overestimated RUP requirements, resulting in predictive losses of milk yield 1.4 to 5.8 times greater than observed values. In summary, the reduction of RDP and RUP proportions did not affect DMI, whereas the RUP reduction at 10% RDP had a small negative effect on energy-corrected milk yield. However, reduction of RDP and RUP consistently improved N-use efficiency of heat-stressed multiparous cows. The reduction of RDP and RUP proportions reduced DMI and milk yield but did not affect energy-corrected milk yield in primiparous cows, indicating a limited supply of nutrients.

Jugular-infused methionine, lysine and branched-chain amino acids does not improve milk production in Holstein cows experiencing heat stress

Poor utilization of amino acids contributes to losses of milk protein yield in dairy cows exposed to heat stress (HS). Our objective was to test the effect of essential amino acids on milk production in lactating dairy cows exposed to short-term HS conditions. To achieve this objective, 12 multiparous, lactating Holstein cows were assigned to two environments (thermoneutral (THN) or HS) from days 1 to 14 in a split-plot type cross-over design. All cows received 0 g/day of essential amino acids from days 1 to 7 (negative control (NC)) followed by an intravenous infusion of l-methionine (12 g/day), l-lysine (21 g/day), l-leucine (35 g/day), l-isoleucine (15 g/day) and l-valine (15 g/day, methionine, lysine and branched-chain amino acids (ML+BCAA)) from days 8 to 14. The basal diet was composed of ryegrass silage and hay, and a concentrate mix. This diet supplied 44 g of methionine, 125 g of lysine, 167 g of leucine, 98 g of isoleucine and 109 g of valine per day to the small intestine of THN cows. Temperature-humidity index was maintained below 66 for the THN environment, whereas the index was maintained above 68, peaking at 76, for 14 continuous h/day for the HS environment. Heat stress conditioning increased the udder temperature from 37.0°C to 39.6°C. Cows that received the ML+BCAA treatment had greater p.m. rectal and vaginal temperatures (0.50°C and 0.40°C, respectively), and respiration rate (8 breaths/min) compared with those on the NC treatment and exposed to a HS environment. However, neither NC nor ML+BCAA affected rectal or vaginal temperatures and respiration rates in the THN environment. Compared with THN, the HS environment reduced dry matter intake (1.48 kg/day), milk yield (2.82 kg/day) and milk protein yield (0.11 kg/day). However, compared with NC, the ML+BCAA treatment increased milk protein percent by 0.07 points. For the THN environment, the ML+BCAA treatment increased concentrations of milk urea nitrogen. For the HS environment, the ML+BCAA treatment decreased plasma concentrations of arginine, ornithine and citrulline; however, differences were not observed for the THN environment. In summary, HS elicited expected changes in production; however, infusions of ML+BCAA failed to increase milk protein yield. Lower dry matter intake and greater heat load in response to ML+BCAA contributed to the lack of response in milk production in HS cows. The ML+BCAA treatment may have reduced the breakdown of muscle protein in heat-stressed cows.

The expression of genes involved in hepatic metabolism is altered by temporary changes to milking frequency

Changes to milking frequency (MF) affect the metabolic and energetic status of dairy cows. However, the duration of altered MF necessary to modify hepatic transcription during early lactation is less clear. Additionally, long-term responses to short-term alterations in MF have not been established. Holstein-Friesian dairy cows (n = 120) were allocated to 3 or 6 wk of either once-daily (1 ×) or thrice-daily (3 ×) milking, immediately postpartum. Following treatment, cows were switched to twice-daily (2 ×) milking. These 4 treatment groups were compared with cows milked 2 × (n = 30) for the whole lactation. Liver tissue was collected by biopsy at 1, 3, 6, and 9 wk postpartum from 12 cows per treatment, RNA was extracted, and transcript abundance of genes involved in hepatic metabolism was quantified. Milking frequency altered the expression of most of the genes measured; however, we observed no effects caused by the length of time on the alternative milking frequency and no interactions between MF and length. During the MF treatment, mRNA expression of some, but not all, genes involved in gluconeogenesis (G6PC, PCK1), fatty acid β-oxidation (CPT1A, CPT2), ketogenesis (HMGCS2), lipid transport (APOA1), and lipolysis (PNPLA2) were lower for cows milked 1 × and plasma glucose and insulin concentrations were greater. Cows milked 3 × had reduced mRNA expression for some of the genes involved in fatty acid synthesis (ACACA) and lipid transport (APOB) and had greater plasma NEFA concentrations at wk 1. At 9 wk postpartum, expression data indicated that cows previously milked 3 × had a greater capacity for gluconeogenesis (PCK1), ketogenesis (HMGCS2), and urea cycling (ASL, CPS1) and lower glucose concentrations than cows previously milked 1 ×, because some of the genes involved in these processes were still altered. Milking cows 1 × relative to 2 ×, however, did not result in significant carryover effects on the expression of the genes measured in this study, indicating that metabolic changes are not sustained beyond the period of reduced MF. Changes to MF altered the hepatic response during early lactation; however, this was not dependent on the duration of MF change. Although we observed only minimal carryover effects on hepatic metabolism from short periods of reduced MF postpartum, there may be long-term effects on urea cycling (ASL, CPS1) and ketogenesis (HMGCS2) when 3 × milking occurs immediately postpartum.

Lowering rumen-degradable and -undegradable protein improved amino acid metabolism and energy utilization in lactating dairy cows exposed to heat stress

The objective of this study was to evaluate the effects of reducing dietary rumen-degradable protein (RDP) and rumen-undegradable protein (RUP) on protein and energy metabolism in heat-stressed dairy cows. Eighteen primiparous and 30 multiparous mid-lactation Holstein cows were used in a completely randomized design arranged in a 2 × 2 factorial (n = 12/treatment). Cows were randomly assigned to 1 of 4 dietary treatments that included 2 levels of RDP (10 and 8%; D) and 2 levels of RUP (8 and 6%; U) of dry matter for 21 d as (1) 10D:8U, (2) 8D:8U, (3) 10D:6U, and (4) 8D:6U. Diets were isoenergetic and contained 50% forage and 50% concentrate (dry matter basis). Cows were housed in a freestall barn. Three weeks before start of treatments, all animals were fed the 10D:8U diet and received supplemental cooling to prevent heat stress. During the treatment period, cows experienced a daily increment in temperature-humidity index from 74 to 82 for 1000 to 2000 h. Blood samples were collected on d -1 and 21 of the treatment period to determine plasma concentrations of AA, glucose, insulin, fatty acids, and β-hydroxybutyrate. For primiparous cows, reducing from 10 to 8% RDP decreased insulin concentrations. For multiparous cows, we found significant RDP by RUP interactions for insulin, β-hydroxybutyrate, fatty acids, total essential AA, and 3-methylhistidine concentrations. Reducing from 10 to 8% RDP decreased insulin concentrations at 6% RUP, but concentrations did not change when reducing RDP at 8% RUP. Reducing from 10 to 8% RDP decreased β-hydroxybutyrate concentrations at 8% RUP, but concentrations did not change when reducing RDP at 6% RUP. Reducing from 10 to 8% RDP increased nonesterified fatty acid and total essential AA concentrations at 8% RUP, but concentrations did not change when reducing RDP at 6% RUP. Reducing from 8 to 6% RUP decreased 3-methylhistidine concentration at 8% RDP, but not at 10% RDP. Reducing from 8 to 6% RUP increased milk protein yield efficiency in primiparous and multiparous cows. These results indicate that reducing RDP and RUP lowers circulating insulin, which was associated with mobilization and utilization of fatty acids. Reduced RDP and RUP increases the use of AA to maintain milk protein synthesis and limit AA catabolism in cows exposed to warm climates.

Gene expression in liver and adipose tissue is altered during and after temporary changes to postpartum milking frequency

Short-term changes to milking frequency can alter the metabolic status of dairy cows depending on the duration, magnitude, and stage of lactation at which the milking frequency changes occur. Additionally, effects of altered milking frequency that are subsequent to cows returning to a normal twice-daily (2×) milking regimen are not well established. This study tested the hypothesis that plasma concentrations of key hormones and metabolites and transcription of genes involved in the somatotropic axis and lipid metabolism would be altered in liver and subcutaneous adipose tissue from cows milked with different frequencies. Multiparous Holstein-Friesian dairy cows were allocated to 2× milking for the whole lactation, or once-(1×) or 3 times-(3×) daily milking for 3 or 6 wk, immediately postpartum, and then 2× milking for the remainder of the lactation. Liver and subcutaneous fat were biopsied at wk 1 (liver only), 3, 6, and 9 postpartum, and transcription of genes involved in the somatotropic axis and lipid metabolism were measured. At wk 3, cows milked 3× had lower hepatic expression of growth hormone receptor (GHR1A) compared with cows milked 2× or 1×, and lower IGF1 expression compared with cows milked 1×, indicating greater uncoupling of the somatotropic axis. At wk 6, reduced transcription of total GHR and GHR1B occurred in the adipose tissue of cows milked 3×. Cows milked 1× had greater transcription in adipose tissue of lipogenesis genes at wk 3 and 6, and lipolysis genes at wk 6, compared with cows milked 2×, indicating a period of increased fatty acid storage, followed by increased fatty acid reesterification. At wk 9, cows previously milked 3× for 6 wk maintained lower transcription of genes involved in lipogenesis, lipolysis, and ketolysis in adipose tissue compared with cows milked 2×, indicating that the effects of 3× milking persist for at least 3 wk after switching to 2× milking. Results indicate that alterations to milking frequency affect the transcription of genes involved in lipid mobilization and storage, enabling the animal to manage the energy demands associated with the change in milk production. Some of these gene transcription changes were maintained in cows previously milked 3×, indicating that the adipose tissue gene expression changes were still required even after 3 wk of the less-demanding 2× milking regimen.

Short communication: Relationships among temperature-humidity index with rectal, udder surface, and vaginal temperatures in lactating dairy cows experiencing heat stress

The objective of this study was to evaluate relationships between measurements of temperature-humidity index (THI) and rectal, vaginal, and udder surface temperatures in lactating cows exposed to heat stress (HS). In experiment 1, 12 multiparous and 8 primiparous Holstein cows experienced a THI ranging from 69 to 76 at 2000 to 1000 h and THI from 74 to 82 at 1000 to 2000 h (peaked at 82 from 1400 to 1800 h). Cows were exposed to HS 10 h daily for 21 d. Measurements of rectal temperature (RT) and udder surface temperature were collected at 1000 and 1500 h (±30 min). Vaginal temperature was monitored every 10 min using digital loggers, averaged over 1 h, and paired with corresponding rectal and udder surface temperature data. In experiment 2, 12 multiparous Holstein cows experienced a THI ranging from 60 to 76 at 2000 to 1000 h and THI from 69 to 83 at 1000 to 2000 h (peaked at 83 from 1600 and 1900 h), eliciting 10 h/d of HS for 7 d. Rectal and udder surface temperatures were analyzed at 0700 and 1500 h (±30 min). Vaginal temperature was recorded and analyzed as indicated in experiment 1. Afternoon THI showed weak correlations with surface temperature (r = 0.19, n = 420 in experiment 1; r = 0.23, n = 84 in experiment 2), weak to moderate correlations with RT (r = 0.34, n = 366 in experiment 1; r = 0.26, n = 84 in experiment 2), and moderate correlations with vaginal temperature (r = 0.34, n = 175 in experiment 1; r = 0.35, n = 40 in experiment 2). Moreover, vaginal temperature increased 0.10 and 0.22°C per unit of THI (R2 = 0.15 in experiment 1; R2 = 0.40 in experiment 2). Afternoon vaginal temperature strongly correlated with RT (r = 0.69, n = 131 in experiment 1; r = 0.63, n = 37 in experiment 2) and explained 57 (experiment 1) and 68% (experiment 2) of variation in RT. Surface temperature showed moderate to strong correlations with RT (r = 0.57, n = 84) and vaginal temperature (r = 0.74, n = 37) in experiment 2. In conclusion, THI showed a weak to moderate relationship with core body temperatures and explained the increase in rectal and vaginal temperatures experienced by HS cows. Compared with rectal temperature, vaginal temperature showed stronger relationships with THI and can be used to determine thermal load. Udder surface temperature showed a moderate to strong relationship with core body temperature, and this relationship may support the use of surface temperature data to manage thermal load in HS cows.