Effects of whole cottonseed, niacin, and niacinamide on in vitro rumen fermentation and on lactating Holstein cows

In Experiment 1, effects of whole cottonseed (0, 5, 15, or 30% of the total ration DM) on in vitro ruminal fermentation showed increased ruminal pH and ammonia concentration but lowered microbial protein. Acetic acid concentration was greatest with diets of 15 and 30% whole cottonseed, but propionate and total VFA concentrations were reduced by increasing whole cottonseed from 0 to 30%. In Experiment 2, neither niacin nor niacinamide (0, 100, 200, or 400 ppm) altered substantially fermenter pH or ammonia concentration. Both niacin and niacinamide increased synthesis of microbial protein. Acetate and propionate concentrations were not altered by treatment. Total VFA concentration tended to be lower as concentration of niacin and niacinamide increased. In Experiment 3, 28 Holstein cows were used to determine the effects of supplemental niacin on feed intake, milk yield, and composition. Cows were fed individually complete mixed diets ad libitum containing either: 1) 0; 2) .015; 3) .03; or 4) .06% niacin. There was a trend for lower milk fat test with niacin supplementation. Milk protein percentage was higher without niacin than with niacin at .015 or .03% in the diet, but daily milk and protein yields were higher with .06% versus .015% of niacin. Supplemental niacin did not affect casein nitrogen, lactose or minerals percentage, or concentrations of plasma glucose and insulin.     

Effects of feeding rations with genetically modified whole cottonseed to lactating Holstein cows

Two experiments were conducted to evaluate dry matter intake (DMI), milk yield, and milk composition from feeding rations that contained different sources of genetically modified whole cottonseed to Argentinean Holstein dairy cows. Twenty-four lactating multiparous Argentinean Holstein dairy cows were used in 2 experiments with a replicated 4 x 4 Latin square design, with cows averaging 565 kg body weight and 53 d in milk at the beginning of the experiments. Treatments in Experiment 1 were: Bollgard cotton containing the cry1Ac gene, Bollgard II cotton containing cry1Ac and cry2Ab genes, Roundup Ready cotton containing the cp4 epsps gene, and a control nongenetically modified but genetically similar cottonseed. In Experiment 2, two commercial sources, a parental control line, and the transgenic cotton containing both cry1Ac and cp4 epsps genes were used as treatments. All cows received the same total mixed ration but with different whole cottonseed sources. Cottonseed was included to provide 2.50 kg per cow daily (dry matter [DM] basis) or about 10% of the total diet DM. The ingredient composition of the total mixed ration was 32% alfalfa hay, 28% corn silage, 22% corn grain, 17% soybean meal, and 2% minerals and vitamins. In addition, genomic DNA was extracted from a subset of milk samples and analyzed by polymerase chain reaction followed by Southern blot hybridization for small fragments of the cry1Ac transgene and an endogenous cotton gene, acp1. No sample was positive for transgenic or plant DNA fragments at the limits of detection for the assays following detailed data evaluation criteria. The DMI, milk yield, milk composition, body weight, and body condition score did not differ among treatments. Cottonseed from genetically modified varieties used in these studies yielded similar performance in lactating dairy cows when compared to non-transgenic control and reference cottonseed.     

A dose-response evaluation of rumen-protected niacin in thermoneutral or heat-stressed lactating Holstein cows

Twenty-four multiparous high-producing dairy cows (40.0 ± 1.4 kg/d) were used in a factorial design to evaluate effects of 2 environments [thermoneutral (TN) and heat stress (HS)] and a dose range of dietary rumen-protected niacin (RPN; 0, 4, 8, or 12 g/d) on body temperature, sweating rate, feed intake, water intake, production parameters, and blood niacin concentrations. Temperature–humidity index values during TN never exceeded 68 (stress threshold), whereas temperature–humidity index values during HS were above 68 for 24 h/d. The HS environment increased hair coat and skin, rectal, and vaginal temperatures; respiration rate; skin and hair coat evaporative heat loss; and water intake and decreased DMI (3.5 kg/d), milk yield (4.1 kg/d), 4% fat-corrected milk (2.7 kg/d), and milk protein yield (181.7 g/d). Sweating rate increased during HS (12.7 g/m² per h) compared with TN, but this increase was only 10% of that reported in summer-acclimated cattle. Niacin supplementation did not affect sweating rate, dry-matter intake, or milk yield in either environment. Rumen-protected niacin increased plasma and milk niacin concentrations in a linear manner. Heat stress reduced niacin concentration in whole blood (7.86 vs. 6.89 μg/mL) but not in milk. Reduced blood niacin concentration was partially corrected by dietary RPN. An interaction existed between dietary RPN and environment; dietary RPN linearly increased water intake in both environments, but the increase was greater during HS conditions. Increasing dietary RPN did not influence skin temperatures. During TN, supplementing 12 g/d of RPN increased hair coat (unshaved skin; 30.3 vs. 31.3°C at 1600 h) but not shaved skin (32.8 vs. 32.9°C at 1600 h) temperature when compared with 0 g/d at all time points, whereas the maximum temperature (18°C) of the room was lower than skin temperature. These data suggest that dietary RPN increased water intake during both TN and HS and hair coat temperature during TN; however, core body temperature was unaffected. Thus, encapsulated niacin did not improve thermotolerance of winter-acclimated lactating dairy cows exposed to moderate thermal stress in Arizona.     

Effect of coating whole cottonseed on performance of lactating dairy cows.

Thirty-six lactating Jersey cows were used in a randomized block design to determine the effect of coating whole fuzzy cottonseed to improve handling characteristics on intake, milk yield, apparent digestibility of nutrients, and blood gossypol concentrations. Treatments included whole cottonseed at 15% of dietary dry matter either as whole cottonseed, whole cottonseed coated with 5% gelatinized corn starch, or whole cottonseed coated with 5% corn starch plus 10% maltodextrin sugar. Dry matter intake, milk yield, percentage of milk protein and lactose, and yield of milk components were not different among treatments; however, the percentage of milk fat was depressed when maltodextrin sugar was included in the coating. When in vitro fermentations of mixed ruminal microorganism were conducted, final pH was lower and concentrations of total fatty acids, propionate, and L-lactate were higher for whole cottonseed coated with starch and sugar compared with uncoated cottonseed. Nutrient intake was similar among treatments, but the apparent digestibility of acid and neutral detergent fiber was reduced when coated cottonseed were fed. Total plasma gossypol concentration was higher for the cottonseed coated with starch compared with cottonseed coated with starch and sugar, but the difference was not of biological significance. Results of this study indicate that coating whole cottonseed with starch does not alter its palatability or nutrient value for supporting milk yield, but a reduction in fiber digestibility was observed. Inclusion of 10% maltodextrin sugar in the coating altered ruminal fermentation and resulted in a depressed percentage of milk fat.     

Effect of lint on whole cottonseed passage and digestibility and diet choice on intake of whole cottonseed by Holstein cows

Effects of rolling whole linted cottonseed and whole acid-delinted cottonseed on whole seed passage and digestibility were determined using 24 lactating Holstein cows. Whole seed passage averaged .74% in all cows fed whole linted seed during the standardization period and .45% in 6 cows fed whole linted seed during a comparison period, contrasted to 11.3% in 6 cows fed acid-delinted seed. Digestibility of ether extract was less in the 6 cows fed whole acid-delinted cottonseed. No advantage was for rolling whole linted cottonseed before feeding, but rolling was beneficial for whole acid-delinted cottonseed. Individual consumption of whole linted cottonseed by 18 nonpregnant, dry Holstein cows varied from .04 to 5.05 kg/day when two-choice options were given for cottonseed versus chopped coastal bermudagrass hay or corn silage, or a complete ration of 75% corn silage and 25% concentrate. No indication of gossypol toxicity was seen, but the large variation in each choice situation suggests it is desirable to blend cottonseed with other ingredients to ensure more uniform consumption.     

Effects of feeding whole cottonseed to lactating dairy cows on glucose and palmitate metabolism

Eight lactating Holstein dairy cows were fed corn silage-based diets with or without whole cottonseed at 18.5% of the dietary dry matter. At 42 days postpartum, a pulse injection of 100 mg glucose/kg body weight was given intravenously and plasma glucose concentration was monitored for 45 min. At 50 d postpartum, biopsies of adipose tissue and mammary tissue were taken and tissue slices were incubated in vitro with either uniform carbon-14 glucose or 1-carbon-14 palmitate. Basal concentration of plasma glucose was not affected by diet, although apparent distribution volume of glucose did seem to decrease due to feeding whole cottonseed. Feeding whole cottonseed decreased uptake of glucose and palmitate in both adipose tissue and mammary tissue and also decreased oxidation of glucose to carbon dioxide in both tissues. Palmitate oxidation was not affected by diet. Incorporation of carbon-14 from glucose into adipose tissue lipids was decreased in cows fed whole cottonseed. Results indicate that fat supplementation in the form of whole cottonseed may decrease palmitate incorporation and glucose utilization for glycerol and reducing equivalent synthesis in both adipose tissue and mammary tissue of lactating dairy cows.     

Effects of encapsulated niacin on evaporative heat loss and body temperature in moderately heat-stressed lactating Holstein cows

Twelve multiparous Holstein cows (145 ± 9 d in milk) were randomly assigned to receive either 0 g/d of encapsulated niacin (control diet; C) or 12 g/d of encapsulated niacin (NI) and were exposed to thermoneutral (TN; 7 d) or heat stress (HS; 7 d) conditions in climate-controlled chambers. The temperature-humidity index during TN conditions never exceeded 72, whereas HS conditions consisted of a circadian temperature range in which the temperature-humidity index exceeded 72 for 12 h/d. Measures of thermal status obtained 4 times/d included respiration rate (RR); rectal temperature; surface temperature of both shaved and unshaved areas at the rump, shoulder, and tail head; vaginal temperature; and evaporative heat loss (EVHL) of the shoulder shaved and unshaved areas. Cows fed NI had increased free plasma niacin concentrations in both the TN and HS periods (1.70 vs. 1.47 ± 0.17 μg/mL). Milk yield did not differ between dietary groups or periods. Dry matter intake was not affected by NI, but decreased (3%) for both C and NI treatments during HS. Water intake was increased during HS in both treatments (C: 40.4 vs. 57.7 ± 0.8 L/d for TN and HS, respectively; NI: 52.7 vs. 57.7 ± 0.8 L/d for TN and HS, respectively). Average EVHL for shaved and unshaved skin for C and NI treatments was higher during HS (90.1 vs. 108.1 g/m² per hour) than TN (20.7 vs. 15.7 ± 4.9 g/m² per hour). Between 1000 and 1600 h, mean EVHL for shaved and unshaved areas for NI fed cows was higher than for C fed cows (106.9 vs. 94.4 ± 4.9 g/m² per hour). The NI fed cows had decreased rectal temperatures during HS compared with the C fed cows (38.17 vs. 38.34 ± 0.07°C) and had lower vaginal temperatures (38.0 vs. 38.4 ± 0.02°C). Calculated metabolic rate decreased during HS regardless of diet (50.25 and 49.70 ± 0.48 kcal/kg of body weight per day for TN and HS, respectively). Feeding NI increased free plasma NI levels, increased EVHL during peak thermal load, and was associated with a small but detectable reduction in rectal and vaginal temperatures in lactating dairy cows experiencing a mild thermal load.     

Performance of lactating dairy cows fed whole cottonseed coated with gelatinized cornstarch.

The handling characteristics of whole cottonseed are improved by coating with gelatinized cornstarch, but limited information is available on the effects of feeding the coated cottonseed to lactating dairy cows. Thirty-six lactating Jersey cows were used in a crossover design trial with 4-wk experimental periods to evaluate the influence of coating whole cottonseed with 2.5% gelatinized cornstarch on dry matter intake, milk yield, and composition. Cows were fed diets containing 10.2% alfalfa-orchardgrass hay, 45.2% corn silage, 15.0% coated or uncoated whole cottonseed, and 29.6% concentrate for ad libitum consumption. Coating whole cottonseed with gelatinized cornstarch tended to reduce dry matter intake, which averaged 16.2 and 15.9 kg/d for uncoated and coated cottonseed, respectively. Milk yield and composition were similar for uncoated and coated cottonseed. The yield of energy-corrected milk per unit of dry matter consumed was greater with coated cottonseed. Cows fed coated cottonseed gained body weight, but cows fed uncoated cottonseed lost weight. Concentrations of plasma urea were similar among treatments; however, NEFA concentrations were lower for cows fed coated whole cottonseed. Results of this trial indicate that coating whole cottonseed with 2.5% gelatinized cornstarch does not alter its feeding value for lactating dairy cows.     

Responses of lactating dairy cows to protected fats or whole cottonseed in low or high forage diets

Thirteen treatments to compare effects of dietary fat on milk yield and composition were control, 15% whole cottonseed, and 2 and 4% Ca-tallowate factorially distributed in low forage (35% corn silage DM) with 14 or 18% CP and high forage (66% corn silage) diets with an additional diet of 8% Ca-tallowate. Different treatments were fed to 36 cows in each of three 28-d periods. Feeding 2 and 4% Ca-tallowate improved milk yield with high forage, although DM intake was slightly depressed; compared with 4% Ca-tallowate, DM intake and milk yield were depressed by 8% Ca-tallowate. Across all diets, whole cottonseed depressed DM intake and milk yield more than when nearly equal fat came from Ca-tallowate (4%). Calcium-tallowate depressed milk fat percentage linearly. Milk fat from cows fed whole cottonseed or Ca-tallowate contained unsaturated fatty acids (mostly C18:1) and lesser quantities of short-chain fatty acids. In a subsequent experiment, Ca-tallowate depressed milk fat percentage, whereas Megalac (calcium salts of fatty acids from palm oil) did not. In a field study, one trial with 210 cows in midlactation showed no effect on milk yield and composition from .54 kg of Megalac/d for 60 d, nor was there any effect detected with 121 cows in early lactation from feeding of .45 kg of Megalac/d for 90 d.     

Effects of whole cottonseed diet and recombinant bovine somatotropin on ovarian follicles in lactating dairy cows

The effects of whole cottonseed (WCS) in the diet and the administration of bovine somatotropin (bST) on ovarian follicular dynamics and plasma progesterone (P4) concentrations were examined in cows during a period of synchronized follicular growth. Lactating Holstein cows (n = 28) were randomly assigned to treatments in a 2 x 2 factorial arrangement. Diets consisted of WCS (15% of dry matter) or no WCS, and bST at a dose of 0 or 208 mg/14 d. Dietary treatments began within 24 h of calving and bST treatments began within 7 d postpartum. Cows received GnRH at 65 +/- 3 d postpartum (d 0), PGF2alpha, (d 7), a second dose of GnRH (d 9), and were inseminated 16 h later (d 10). Ovarian changes were monitored daily by ultrasonography from d 0 to 9. On d 9,93% of cows had a preovulatory follicle and 86% ovulated. For Class 2 (6 to 9 mm) follicles, a diet x bST interaction was detected, with bST stimulating Class 2 follicles in cows fed WCS, but not in cows on the control diet. Neither diet nor bST affected numbers of Class 1 (2 to 5 mm) or Class 3 (> or = 10 mm) follicles or sizes of the subordinate and dominant follicles. During the luteal phase of the cycle, lactating cows fed WCS tended to have elevated concentrations of plasma P4, whereas bST was without effect. Plasma concentrations of high-density lipoprotein cholesterol were increased in cows fed WCS. Number and diameter of corpora lutea did not differ among treatments.     

Physiological effects of whole cottonseed in the diet of lactating dairy cows

With 32 lactating Holstein cows we evaluated physiological effects of gossypol and cyclopropenoid fatty acids in diets containing 18.5% whole cottonseed (dry matter) based on corn, corn silage, and soybean meal. All cows consumed a control diet for the first 2 wk of lactation and then were assigned to either control or whole cottonseed diet for the remainder of their lactation. Milk production, milk fat and protein percentages, and daily dry matter intake were measured. Dry matter intakes were less for cows consuming the whole cottonseed diet, but net energy intake was similar for all diets. Milk fat from cows consuming whole cottonseed contained detectable concentrations of cyclopropene fatty acids. Total lipid in plasma, total serum cholesterol, serum gossypol, and apparent liver gossypol concentrations were greater in cows fed whole cottonseed. Gossypol and cyclopropenoid fatty acids appeared to be absorbed from the gut of cows fed whole cottonseed. Small amounts of gossypol in serum and liver tissue and small amounts of cyclopropene fatty acids in adipose tissue lipids and milk fat indicate a need to elucidate the significance of these physiologically active compounds in the human diet and their biological effects on lactating dairy cows.     

Effects of feeding crude glycerin on performance and ruminal kinetics of lactating Holstein cows fed corn silage- or cottonseed hull-based, low-fiber diets

The objective was to determine whether crude glycerin could partially replace concentrate ingredients in corn silage- or cottonseed hull-based diets formulated to support minimal milk fat production without reducing milk production. Multiparous, lactating Holstein cows (n=24; 116 ± 13d in milk) were assigned to dietary treatments arranged in a 2 × 3 factorial design; namely, 2 dietary roughage sources (cottonseed hulls or corn silage) and 3 dietary concentrations of glycerin [0, 5, or 10% on a dry matter (DM) basis]. Four different cows received each dietary treatment in each of 3 periods such that each diet was evaluated using 12 cows. Crude glycerin, produced using soybean oil, contained 12% water, 5% oil, 6.8% sodium chloride, and 0.4% methanol. Glycerin partially replaced ground corn, corn gluten feed, and citrus pulp. Diets of minimum fiber concentrations were fed to lactating dairy cows and resulted in low concentrations of milk fat (averaging 3.12% for cows fed diets without glycerin). The effects of glycerin on cow performance and ruminal measurements were the same for both dietary roughage sources with the exception of feed efficiency. Replacing concentrate with crude glycerin at 5% of dietary DM increased DM intake without increasing milk yield. Concentration and yield of milk fat were reduced when glycerin was fed at 10% of dietary DM. This was accompanied by a 30% reduction in apparent total-tract digestion of dietary neutral detergent fiber. Crude glycerin affected the microbial population in the rumen as evidenced by increased molar proportions of propionic, butyric, and valeric acids and decreased molar proportions of acetic acid. Efficiency of N utilization was improved as evidenced by lower concentrations of blood urea nitrogen and ruminal ammonia-N. Cows fed cottonseed hull-based diets consumed 5.3 kg/d more DM but produced only 1.7 kg/d more milk, resulting in reduced efficiency. Increased production of ruminal microbial protein, molar proportion of propionic acid, and passage of ruminal fluid resulted from feeding the cottonseed hull- versus corn silage-based diets, although apparent digestibilities of DM and neutral detergent fiber were reduced. Replacing 5 and 10% of concentrate ingredients with crude glycerin improved efficiency of 4% fat-corrected milk production when corn silage-based diets were fed but decreased it when cottonseed hull-based diets were fed.     

The effects of feeding varying amounts of gossypol from whole cottonseed and cottonseed meal in lactating dairy cows.

Effects of feeding varying amounts of total gossypol from whole cottonseed and cottonseed meal were evaluated in 30 lactating Holstein cows. After a 14-d pretreatment period, cows were assigned for 42 d to one of five treatments: control (diet A); 1040 mg/kg of total gossypol, and 989 mg/kg of free gossypol from whole cottonseed (diet B); 900 mg/kg of total gossypol and 64 mg/kg of free gossypol from cottonseed meal (diet C); 960 mg/kg of total gossypol and 531 mg/kg of free gossypol with equal amounts of total gossypol from whole cottonseed and cottonseed meal (diet D); or 1922 mg/kg of total gossypol and 1050 mg/kg of free gossypol with equal amounts of total gossypol from whole cottonseed and cottonseed meal (diet E). Concentrations of plasma gossypol and its isomers were directly proportional to free gossypol intake. Plasma gossypol concentrations plateaued after 35 d on treatment, and they were highest in cows receiving diet E. At 42 d on treatment, erythrocyte fragility was higher in the cows receiving the diet E, but it did not differ among other treatments. Dry matter intakes were similar for all groups. Cows receiving diet E produced more milk and 3.5% fat-corrected milk, but milk protein content decreased. Feeding diets containing 1900 mg/kg of total gossypol and 1050 mg/kg of free gossypol for 42 d resulted in increased plasma gossypol concentrations and erythrocyte fragility, but no detrimental impact on lactation performance were observed.     

Performance of lactating dairy cows fed whole cottonseed coated with gelatinized starch plus urea or yeast culture

Thirty lactating Holstein cows were used in an 8-wk randomized design trial to test the viability of select additives included in the gelatinized corn starch coating applied to whole cottonseed (WCS) on nutrient intake and digestibility and milk yield and composition. Treatments included WCS coated with 2.5% gelatinized corn starch (control); control plus 0.5% urea; or control plus 2.0% yeast culture. The treated WCS represented 12.6% of the dietary dry matter. Cellulose intake was lower for the control coating compared with either the urea or yeast coating because of slightly lower cellulose concentrations in the control treatment. Intake of all other nutrients was similar for all treatments. Whole-tract nutrient apparent digestibility was not altered by treatment. Dry matter intake and milk yield were similar among treatments. Percentage solids-not-fat was lower for the yeast treatment compared with control, but no other differences were observed in milk composition among treatments. Efficiency of milk production (energy-corrected milk yield per unit of dry matter intake) was higher for the urea and yeast treatments compared with control because of slightly higher yield of milk fat and energy-corrected milk. No differences were observed in body weight change during the trial between treatments. Results of this trial indicate that including urea or yeast culture in the gelatinized starch coating does not change whole tract digestibility, but does improve milk production efficiency.     

Effects of a supplemental yeast culture on heat-stressed lactating Holstein cows

Multiparous, lactating Holstein cows (n = 23; 120 ± 30 d in milk, 690 ± 67 kg of body weight) housed in climatic chambers were randomly assigned to 1 of 2 dietary treatments: a diet containing a novel yeast culture formulation (YC) for heat stress (n = 12, 10 g/d) or a control diet (n = 11). The trial length was 28 d and consisted of a 7-d thermal neutral period (TN; 18°C, 20% humidity) followed by 21 d of heat stress (HS; cyclical daily temperatures ranging from 29.4 to 37.8°C and 20% humidity). Cows were individually fed a total mixed ration consisting primarily of alfalfa hay and steam-flaked corn. During TN, the YC feeding had no effect on production variables or most body temperature indices. During HS, all body temperature indices increased and YC had no effect on rump surface temperature, respiration rate, or sweating rates. Cows fed YC had lower rectal temperatures at 1200 and 1800 h (40.29 vs. 40.02°C and 40.35 vs. 40.12 ± 0.07°C, respectively) compared with control-fed cows. Cows fed both diets lost body weight (42 kg) during HS, but there were no differences between diets. Control-fed cows had increased dry matter intake (DMI) and milk yield (19.1 vs. 17.9 ± 0.5 kg/d and 32.15 vs. 29.15 ± 0.02 kg/d, respectively) compared with YC-fed cows, but intake and milk production were similar between diets when evaluated on a body weight basis. Heat stress progressively decreased DMI (29%) and milk yield, with milk production reaching a nadir (33%) in the third week. Heat stress decreased milk protein (7%) and lactose (5%) levels, but did not alter milk fat content. Heat-stressed cows were in calculated negative energy balance (−1.91 ± 0.70 Mcal/d) and this was unaffected by diet. Independent of diet, HS decreased plasma glucose (11%), but neither diet nor HS altered basal nonesterified fatty acid levels. Heat stress increased plasma urea N concentrations (11.5 vs. 14.8 ± 0.4 mg/dL). Despite YC-fed cows having slightly reduced body temperatures indices, feeding YC did not prevent the negative effects of HS.     

Digestibility in lactating cows of diets containing whole Pima treated with sodium hydroxide versus Akala or Pima cottonseed

This study examines the effect of NaOH treatment on the nutritive value of Pima cottonseed for lactating cows. Treatment of Pima cottonseed with NaOH increased the extent of dry matter (DM) and neutral detergent fiber in vitro digestibility. Three groups of cows were fed 3 similar total mixed rations (TMR) differing only in the type of cottonseed fed, either whole linted Akala, whole unlinted Pima, or whole Pima treated with 4% NaOH (T-Pima). Dry matter and organic matter (OM) intakes of Akala and Pima TMR were similar and tended to be lower compared with cows fed T-Pima. This was reflected in similar intake of crude protein and lipids by cows fed the 3 TMR. Digestibility of DM, OM, and crude protein were similar in cows fed Pima and T-Pima diets, and slightly higher in cows fed the Akala TMR. Lipid digestibility was highest in cows fed Akala TMR, whereas cellulose and NDF digestibility were lowest in Pima TMR. In the 3 TMR, there was a large gap between the high values of "digestibility of intact seeds" and actual in vivo digestion of DM and OM. Similar yields of milk and milk protein were obtained in cows fed the Akala and Pima TMR, whereas higher yields of milk, milk protein, milk fat, and 4% fat-corrected milk were found in the T-Pima cows. Similar efficiency of DM intake for fat-corrected milk production was achieved by cows fed the 3 TMR.     

Effects of heat stress on energetic metabolism in lactating Holstein cows

Heat stress has an enormous economic impact on the global dairy industry, but the mechanisms by which hyperthermia negatively affect systemic physiology and milk synthesis are not clear. Study objectives were to evaluate production parameters and metabolic variables in lactating dairy cows during short-term heat stress or pair-fed conditions coupled with bST administration. Twenty-two multiparous Holstein cows were subjected to 3 experimental periods: 1) thermoneutral conditions with ad libitum intake for 7 d (P1); 2) heat stress (HS) with ad libitum intake (n = 10) or pair-fed (PF) in thermoneutral conditions (n = 12) for 7 d (P2), and 3) 7 d of HS or PF in conditions as described in P2 with recombinant bovine somatotropin administered on d 1 (P3). All cows received an intravenous glucose tolerance test (GTT) on d 5 of each period. Heat stress conditions were cyclical and temperatures ranged from 29.4 to 38.9°C. Rectal temperatures and respiration rates increased during heat stress (38.6-40.4°C and 44-89 breaths/min, respectively). Heat stress reduced dry matter intake by 30% and by design PF cows had similar intake reductions (28%). During heat stress and pair-feeding, milk yield decreased by 27.6% (9.6 kg) and 13.9% (4.8 kg), respectively, indicating that reduced feed intake accounted for only 50% of the decreased milk production. Milk yield increased with recombinant bovine somatotropin in both HS (9.7%) and PF (16.1%) cows. Cows in both groups were in positive energy balance (3.95 Mcal/d) during P1 but entered negative energy balance during P2 and P3 (−5.65 Mcal/d). Heat stress and pair-feeding treatments decreased (9.3%) basal glucose concentrations. Heat stress conditions had no effect on basal NEFA levels during P2; however, PF cows (despite a similar calculated energy balance) had a 2-fold increase in basal NEFA concentrations. Both groups had increased plasma urea nitrogen levels during P2 and P3 compared with P1. Basal insulin levels increased (37%) during P2 and P3 in HS cows but did not differ between periods in PF cows. During P2 and compared with P1, PF cows had a decreased rate of glucose disposal, whereas HS cows had a similar disposal rate following the GTT. During P2 and compared with P1, PF cows had a reduced insulin response whereas HS cows had a similar insulin response to the GTT. In summary, reduced nutrient intake accounted for only 50% of heat stress-induced decreases in milk yield, and feed intake-independent shifts in postabsorptive glucose and lipid homeostasis may contribute to the additional reduction in milk yield.     

Effects of differences in starch content of diets with whole cottonseed or rice bran on milk casein

Forty lactating Holstein cows in early to midlactation were used in a randomized complete block design to measure the effects of the following diets on milk casein. Treatments were four complete rations fed for ad libitum intake consisting of 1) 60% concentrate, 10% alfalfa hay, and 30% corn silage; 2) 45% concentrate, 10% alfalfa hay, 30% corn silage, and 15% whole cottonseed; 3) 60% concentrate, 5% alfalfa hay, 20% corn silage, and 15% whole cottonseed; and 4) 45% concentrate, 10% alfalfa hay, 30% corn silage, and 15% rice bran. Least squares means for daily DM intake all were significantly different and were 3.51, 3.90, 3.28, and 3.74% BW, respectively. Cows fed diet 3 had higher arterial glucose and insulin and venous insulin. Least squares means were significantly different for milk yield, 30.1, 31.4, 28.4, and 31.6 kg/d; for milk protein, 3.30, 3.13, 3.48, and 3.12%; and for casein N, .376, .358, 3.73, and .330, respectively. However, milk protein and casein N yields were similar for all cows. The diet that contained the highest percentage of starch did not result in a significantly higher percentage of casein N in the milk but had the lowest milk production. Both whole cottonseed and rice bran, substituted for concentrate, depressed milk protein percentage.     

The effects of varying gossypol intake from whole cottonseed and cottonseed meal on lactation and blood parameters in lactating dairy cows

Effects of varying amounts of gossypol from whole Upland cottonseed (WCS) and cottonseed meal (CSM) were evaluated in 40 midlactation Holstein cows. After 14 d of pretreatment, cows were assigned to 1 of the 5 treatments for 84 d: control (no gossypol), 931 mg/kg total gossypol (TG) and 850 mg/kg free gossypol (FG) from WCS (moderate TG and high FG); 924 mg/kg TG and 91 mg/kg FG from CSM (moderate TG and low FG), 945 mg/kg TG and 479 mg/kg FG with equal amounts of TG from WCS and CSM (moderate TG and FG), or 1894 mg/kg TG and 960 mg/kg FG with equal amounts of TG from WCS and CSM (high TG and FG). Concentrations of plasma gossypol (PG) and its isomers were directly proportional to FG intake. Concentrations of PG reached a plateau after 28 d on treatment, and they were highest in cows receiving a diet with high TG and FG. Erythrocyte fragility differed among treatments and increased with increasing FG intake. Plasma gossypol returned to negligible concentrations 28 d after withdrawal of cottonseed products from the high TG and FG diet. Serum vitamin A was similar among treatments, but vitamin E increased with increasing FG intake. Serum enzymes were generally unaffected by treatments, but urea N increased in diets higher in TG and FG. Intake of dry matter was higher for the diet high in TG and FG than for the control diet, but was similar for other treatments. Cows receiving the high TG and FG diet produced more milk and 3.5% fat-corrected milk, with no changes in milk composition. Feeding a diet containing 1894 mg/kg TG and 960 mg/kg FG for 84 d increased PG concentrations and erythrocyte fragility and resulted in minor changes in blood metabolites and enzymes, but no detrimental effect on lactation performance was observed. Indicators of liver, kidney, and muscle cell viability suggest that the higher amounts of gossypol consumed in this study had only minor effects on those tissues in lactating dairy cows.     

Methane prediction in dry and lactating Holstein cows.

Data from six experiments (two with dry cows) were used to predict partitioning of gross energy to CH4 in Holstein cows using selected independent variables, some of which were intercorrelated, and a stepwise backward elimination regression procedure. Methane outputs ranged from 3.1 to 8.3% (mean 5.5) of gross energy intake for 134 dry cow balance trials and from 1.7 to 14.9% (mean 5.2) of gross energy intake for 358 lactating cow energy balance trials. This is equivalent to 176 and 300 g/d or 245 and 419 L/d of CH4 for dry and lactating Holstein cows, respectively. Digestibilites of hemicellulose and neutral detergent solubles were positive predictors, and cellulose digestibility was a negative predictor of CH4 output in dry cows fed all forage diets, but hemicellulose digestibility was not a significant variable for predicting CH4 production by lactating cows fed diets with concentrate and forages. Fiber digestibility generally remained in models to predict CH4 output. Except for one data set, regression equations accounted for 50 to 72% of the variation in percentage of gross energy partitioned to CH4 by Holstein cows. Results confirm that increased concentrate feeding reduces CH4 production. Supplementation of lactation diets with fat generally increases fat digestibility, and this trait was associated with reduced CH4 output. Results enable 1) estimation of CH4 output for calculation of metabolizable energy and 2) computation of the contribution from dairy cows to global warming.