Stochastic models for simulating parallel, rotary, and side-opening milking parlors.

Simulation models of parallel, rotary, and side-opening milking parlors were built that could predict milking parlor performance according to herd size, number of milking stalls, labor quality, and cow characteristics. The models were validated by statistically comparing the duration of the simulated milking process with actual data collected at 3 dairy farms during 12 mo. Various scenarios were generated to study parlor performance, and the results indicated that for a parlor with up to 14 milking stalls, a side-opening design provided greater capacity than parallel or rotary parlors. Performance of a side-opening parlor was reduced by enlargement up to 20 milking stalls. For 10 to 40 milking stalls, a rotary design gave better performance than a double parallel design in terms of milking process duration and stall utilization. The presented models can serve as a practical tool in designing new parlors or changing operations of existing ones.

Effect of nursing management and skeletal size at weaning on puberty, skeletal growth rate, and milk production during first lactation of dairy heifers.

Forty Israeli-Holstein 5-d-old calves were used to determine the effect of increasing calf body weight (BW) and skeletal size during the nursing period on age and skeletal size at puberty and on skeletal size and performance during first lactation. The calves were randomly allotted to 2 experimental groups as follows: milk replacer (MR) [calves were given 0.450 kg/d dry matter of milk replacer for the first 50 d of life] and milk-fed (MF) [calves had free access to milk in two 30-min meals/d]. From weaning to 180 d of age, all calves were fed the same diet. At 180 d of age, the MR and MF calves were each divided into 2 equal subgroups: one subgroup from each treatment was given only growing ration, and the other was given the same ration supplemented with fish meal to supply 2% crude protein (CP) (treatments MR + CP and MF + CP, respectively). Finally, at 270 d of age, all calves were housed together and fed a growing heifer's ration until first calving. During the entire nursing period, the MF calves consumed 9.8% more DM, 39.7% more CP, and 52.4% more metabolizable energy than the MR calves. At 60 d of age, BW and all skeletal parameters were higher in the MF calves than in the MR calves. During the entire rearing period (60 to 550 d), the average BW of the MF calves was greater by 16 kg than the BW of the MR calves. Nursing management did not affect differences in skeletal parameters at calving. Average age at puberty onset was 272 +/- 26.8 d; MF calves reached puberty 23 d earlier than MR calves. Yields of milk (kg/305 d) and fat-corrected milk (FCM, kg/d) were greater for the MF + CP heifers than for the MR heifers. It was concluded that nursing by ad libitum milk, as compared with milk replacer, affected BW but not skeletal size of the adult animal, decreased age of puberty onset, and increased FCM yield at first lactation. Supplementing the diet with 2% CP during the prepubertal period increased BW but not skeletal size of the adult animal and 305-d milk and FCM yields during first lactation.

The effect of protein intake on performance of cows in hot environmental temperatures.

Two trials were conducted with cows in commercial herds during midlactation to evaluate the effect of dietary crude protein (CP) concentration on the production, composition, and efficiency of milk production under hot ambient conditions. Cows were group-fed in trial 1, which was conducted in two herds, and were fed individually in trial 2. The respective average ambient temperature, relative humidity, and temperature-humidity index (THI) were 31 degrees C, 45%, and 78 in trial 1 and 27 degrees C, 70%, and 76 in trial 2. Cows were cooled by forced evaporative means six times daily in trial 1 and three times daily in trial 2. Dietary CP was 15.3 or 17.3% of dry matter (DM) in trial 1 and 15.1 or 16.7% of DM in trial 2. The respective ratios of rumen-degradable organic matter (RDOM) to rumen-degradable protein were 5.3 and 4.8 for the low CP (LP) and high CP (HP) diets. Average DM intake, milk yield, and milk fat and protein concentrations were 22 and 23 kg/d, 34 and 35 kg/d, 3.1 and 3.4%, and 3.2 and 3.1% in trials 1 and 2, respectively, and were similar among diets in both trials. The resultant calculated milk protein efficiency ratio and overall CP efficiency were 0.31 and 0.32 for the LP diets and 0.28 and 0.29 for the HP diets. In cows fed the LP diet, diet rumen ammonia was lower in trial 1, and milk urea N was lower in trial 2. The BW change was higher in trial 1, and tended to be higher in trial 2, with the LP diets. Changes in body condition score in trials 1 and 2 tended to be higher with the LP diets. It was concluded that a dietary CP content of 15.3% is adequate to maintain production in heat-exposed dairy cows producing 35 kg of milk/d, provided that the forced evaporative cooling and the ratio of RDOM to rumen-degradable protein is appropriate

Effect of site and source of energy supplementation on milk yield in dairy cows.

The effect of infusing similar energy equivalents of starch into the rumen, or starch or oil into the abomasum was studied in four midlactation cows in a 4 x 4 Latin square design experiment; controls were ruminally infused with water. Cows were fitted with cannulas in the rumen, abomasum, and ileum, and nutrient digestion in the rumen and small intestine was evaluated with Cr as a digesta marker. Ruminal infusions of starch, or abomasal infusions of starch or oil, were associated with a decrease in voluntary feed organic matter intake. Overall energy intake was reduced in oil-infused, but not in starch-infused cows. Nonstructural carbohydrate digestibility in the rumen and in the small intestine was similar among treatments. In abomasally infused cows 3.4 kg/d of nonstructural carbohydrates was apparently digested in the small intestine. Milk production was reduced in oil-infused cows, but the efficiency of milk energy and protein yield was unaffected by treatments. Plasma glucose, insulin, and IGF-1 concentration, mammary glucose extraction rate, rumen ammonia and plasma urea, and arterial and mammary extraction rate of amino acids were all similar among treatments. Large quantities of starch can be digested in the rumen or small intestine of dairy cows. There appear to be no metabolic advantage to increasing the supply of starch to the rumen or the abomasum of mid-lactation dairy cows maintained on highly concentrated diets and exhibiting a positive energy balance.

Preovulatory follicular status and diet affect the insulin and glucose content of follicles in high-yielding dairy cows.

Insulin and glucose may be limiting factors for ovarian function in dairy cows genetically selected for high milk yield. The effects of nutrition on the intrafollicular content of insulin and glucose were investigated in Israeli Holstein dairy cattle fed a basic total mixed ration and producing 34-39kg of milk daily. In experiment 1, carried out in 11 oestrus-synchronised cows, little variation in insulin concentration was found in plasma sampled during the luteal phase, but high variation was found in plasma sampled during the follicular phase. Therefore, in order to prevent confounding the effects of diet and of phase in cycle in the following experiments, experimental diets were fed during the luteal phase of synchronised oestrus cycles. In experiment 2, designed as Latin-Square, six cows received sequentially diets containing 17.1 (control) or 19.7% of crude protein, using two sources of supplementary protein, i.e. soyabean meal (SBM) and corn gluten meal (CGM), differing in ruminal degradability and leucine content. When dry matter intake was used as covariant, plasma insulin on day 16 was 29.5 and 26.4% higher in cows fed diets containing SBM and CGM than in the control (P<0.05). In experiment 3, 17 cows were individually fed the basic diet and then switched to isoenergetic diets containing SBM (n=5), CGM (n=6) or corn grain (CG, n=6) given from day 10 to 16 of the synchronised oestrus cycle. On the eve of day 16, and in the morning of day 17, they were administered PGF(2alpha) and the content of 26 largest follicles was aspirated by using the transvaginal ovum pick-up technique. Follicles were sorted into two classes (preovulatory and subordinate) according to oestradiol concentration and the progesterone:oestradiol ratio in follicular fluid (FF). Higher concentrations of insulin (0.282 versus 0.127ng/ml, P<0.0001) and of glucose (0.614 versus 0.386g/l, P<0.002), were found in FF from preovulatory follicles. The insulin concentration in the FF of cows fed the CG diet was 26% higher than in their counterparts fed CGM (P<0.04), SBM being intermediate. Dietary effects did not reach significance in subordinate follicles. The finding that preovulatory follicular status is associated with increased intrafollicular insulin and glucose suggests that insulin is involved in follicular maturation. The nutritional effect on intrafollicular glucose and insulin may have practical implications to optimise feeding in dairy cows during phases of the oestrus cycle.

Mammary lipogenic enzyme activity, trans fatty acids and conjugated linoleic acids are altered in lactating dairy cows fed a milk fat-depressing diet.

The objectives of the present study were to examine the effect of a milk fat-depressing (MFD) diet on: 1) the activity of mammary acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), 2) ACC mRNA relative abundance and 3) distributions of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA) in milk fat. Twelve lactating Holstein cows were used in a single reversal design. Two diets were fed: a control diet (60:40% forage/concentrate) and an MFD diet (25:70% forage/concentrate, supplemented with 5% soybean oil). The MFD diet decreased (P: < 0 0.001) milk fat by 43% and ACC and FAS activity by 61 and 44%, respectively. A reduced ACC mRNA relative abundance (P: < 0.001) corresponded with the lower ACC activity. The fatty acids synthesized de novo were decreased (P: < 0. 002), whereas tFA were increased from 1.9 to 15.6% due predominantly to a change in trans-10-18:1 isomer (P: < 0.001). With the MFD diet, the trans-7, cis-9 and trans-10, cis-12 CLA isomers were elevated (P: < 0.001), in contrast to the decrease in trans-11-18:1 (P: < 0. 001) and cis-9, trans-11-18:2. The data were consistent with a dietary effect on mammary de novo FA synthesis mediated through a reduction in ACC and FAS activity and in ACC mRNA abundance. The results were compatible with a role of trans-10, cis-12 CLA in milk fat depression, but alterations noted in tFA and other CLA isomers suggest that they also may be important during diet-induced milk fat depression.

Partitioning of amino acids flowing to the abomasum into feed, bacterial, protozoal, and endogenous fractions.

We partitioned the flow of amino acids (AA) to the abomasum among rumen undegradable protein (RUP) and bacterial, protozoal, and endogenous fractions using four Holstein cows in midlactation that were equipped with ruminal and abomasal cannulas. A 2 x 2 factorial design with four diets, combinations of high or low ruminally degradable organic matter, and rumen degradable protein, was employed. Crude protein (CP) and AA contents of ruminal bacteria and protozoa and abomasal digesta were determined. Equations for the source compositions and in vivo flows of CP and 16 AA were then solved simultaneously with a linear program to estimate the contribution of RUP, bacterial, protozoal, and endogenous CP to AA flows. The flows of RUP and bacterial AA were not affected by diet. Low dietary RDP increased the flow of protozoal AA to the abomasum, but the ruminally degradable organic matter content of the diet did not affect protozoal AA flow. Across diets, RUP, bacterial, protozoal, and endogenous fractions provided 55, 33, 11, and <1% of the CP, and 62, 26, 12, and <1% of the AA that reached the abomasum. The linear program was a useful tool for partitioning AA that flows to the abomasum. The technique may also allow dietary effects on ruminal microbes and the AA profile of protein flowing to the duodenum to be better understood and perhaps manipulated.

Effects of extrusion of grain and feeding frequency on rumen fermentation, nutrient digestibility, and milk yield and composition in dairy cows.

The effect of corn extrusion and feeding frequency on ruminal and postruminal digestibility and milk yield was studied in cows fed a high concentrate diet. Four Israeli Holstein cows fitted with rumen and abomasal cannulas were used. The experiment was arranged as a 2 x 2 factorial design, with two diets and two feeding frequencies (two or four meals per day). One diet contained 40% ground corn. In the second diet, half of the ground corn was replaced with extruded corn. Feeding cows the extruded versus ground corn diet decreased ruminal ammonia N and plasma urea N concentrations, increased postruminal digestibility of nonstructural carbohydrates, reduced dry matter intake, decreased yield of milk and milk components, and increased efficiency of milk energy and milk protein synthesis. The inclusion of extruded corn in the diet did not affect ruminal volatile fatty acid. Increasing the feeding frequency reduced the diurnal variation in ruminal pH, ruminal ammonia, and plasma urea, and increased dry matter intake--considerably more in the cows fed ground versus extruded corn--and improved postruminal organic matter, nonstructural carbohydrate, and crude protein digestibility. Total tract digestibility of organic matter and crude protein and milk yield and composition were also increased when cows were fed four versus two meals. Concurrent with the feeding frequency and grain processing effect, an increase in rumen-undegradable protein flow was related to increased digestion of nonstructural carbohydrate postruminally (r = 0.54). We concluded that for cows fed high-starch diets more frequent meals are useful for improving postruminal digestibility and milk yield and composition.

Heat-treated whole cottonseed: effect of dietary protein concentration on the performance and amino acid utilization by the mammary gland of dairy cows.

The effects of replacing whole cottonseed by heated whole cottonseed at two levels of crude protein on amino acid (AA) utilization by the bovine mammary gland were investigated. Four Israeli Holstein cows were used in a 4 x 4 Latin square design with 2 x 2 factorial arrangements. Diets were formulated to contain two levels of crude protein (CP), normal (160 g CP/kg dry matter) and low (140 g CP/kg dry matter), and two levels of rumen undegradable protein (UDP), high (380 g UDP/kg CP) and low (350 g UDP/kg CP). Whole cottonseed was quantitatively substituted by heated whole cottonseed to formulate the high UDP diets. Intakes of dry matter and organic matter were similar for all treatments and averaged 15.9 and 14.4 kg/d respectively. Yields of milk and its constituents were similar for all treatments. Milk yield averaged 23.1 kg/d and this contained (per kg) 32.3 g CP, 25.4 g total casein and 47.5 g lactose. The milk fat content was lower in the cows given the high UDP diets, averaging 34.6 g/kg compared with 38.9 g/kg in the cows fed on the diets with low UDP. Plasma AA concentrations were similar for all treatments apart from Leu and Ile, which were higher in the cows given the high CP diets: 152 and 103 microM compared with 183.8 and 131.5 microM for the low CP diets. Net extraction and balance of essential AA across the half udder suggested that essential AA were supplied in amounts sufficient to meet milk protein requirements for all treatments. The surplus AA supplied as a result of feeding the high dietary CP were probably catabolized via an enhanced oxidative pathway, possibly in the liver, presumably as a passive response to their disposal.

In situ assessment of degradability of organic matter in the rumen of the dairy cow.

This study analyzed the relationships among the effective degradabilities of organic matter (OM) in feedstuffs, which were assessed separately by an in situ method and a direct in vivo measurement of the rumen degradation of OM in the diets of Holstein dairy cows. For this comparison, 80 individual data points were used from studies of dairy cows that were in midlactation and that had been cannulated in the rumen and abomasum. In vivo evaluation of the true degradability of OM in the rumen was based on rare earth digesta markers. Purine N served as a microbial marker. Feed samples were incubated in the rumens of dairy cows for 3, 6, 9, 12, 24, 48, and 72 h, and effective rumen degradation was calculated from the percentage of residual OM for rumen outflow rates of 4, 6, and 8%/h. Evaluations of rumen degradability of OM by the in situ method were correlated with actual in vivo measurements of rumen degradability of OM (r2 = 0.31, 0.34, and 0.37; SE of the estimate = 4.1, 4.0, and 3.9%, respectively). We concluded that the in situ method is a useful tool for providing reliable estimates of rumen degradability of OM in dairy cows.

Effect of the synchronization of the degradation of dietary crude protein and organic matter and feeding frequency on ruminal fermentation and flow of digesta in the abomasum of dairy cows.

Four Holstein cows in midlactation were equipped with ruminal and abomasal cannulas and used to study the effect of synchronized degradation of crude protein (CP) and organic matter (OM) and feeding frequency on digestion and outflow of nutrients. A 4 x 4 Latin square design was used. Diets were arranged in a 2 x 2 factorial design; the four diets contained high ruminally degradable OM and high ruminally degradable CP, high ruminally degradable OM and low ruminally degradable CP, low ruminally degradable OM and high ruminally degradable CP, and low ruminally degradable OM and low ruminally degradable CP. In each period, cows were fed four times daily from d 1 to 14 and two times daily from d 15 to 28. Mean daily ruminal ammonia N concentration was reduced by high ruminally degradable OM, low ruminally degradable CP, and twice daily feeding. Fluctuation in ruminal ammonia N was lower when cows were fed four times daily than when cows were fed twice daily. Plasma urea N concentrations were lower for cows fed diets that were high in ruminally degradable CP. Higher CP flow in the abomasum was found for cows fed the diet containing high ruminally degradable OM and low ruminally degradable CP. Microbial dry matter and CP flow to the abomasum were higher for cows fed twice daily than for cows fed four times daily. Flow of OM in the abomasum was not altered by concentrations of ruminally degradable OM or CP. These results suggest that the available energy in the rumen (ruminally degradable OM) is the most limiting factor for ruminal N utilization under our experimental conditions. Use of these data may improve the prediction of plasma urea N.

The effect of enhanced milk yield of dairy cows by frequent milking or suckling on intake and digestibility of the diet.

Groups of 9 or 10 cows were assigned to one of three treatments 1) machine-milking three times daily, 2) machine-milking six times daily, and 3) suckling three times daily in addition to machine-milking three times daily. Treatments were conducted during the first 6 wk postpartum. During wk 5, digestibility of the diet was estimated by the indigestible neutral detergent fiber method. During wk 6, milk yield and dry matter intake (DMI) were recorded daily, and plasma concentrations of glucose, nonesterified fatty acids, urea, protein, growth hormone, insulin, insulin-like growth factor I, oxytocin, and prolactin were determined. Milk yields were 38.5, 46.8, and 52.7 kg/d, and DMI were 18.1, 21.2, and 17.2, for cows on treatments 1, 2, and 3, respectively. Plasma glucose concentrations decreased, and plasma nonesterified fatty acid concentrations increased, for cows on treatments 2 and 3 compared with cows on treatment 1. Digestibility of dry matter was 57.5, 60.5, and 60.6%; of organic matter was 62.6, 64.6, and 66.8%; and of crude protein was 59.3, 62.7, and 64.6% for cows on treatments 1, 2, and 3, respectively. Concentrations of all assayed hormones, except insulin, increased moderately for cows on treatment 2 compared with cows on treatment 1 and increased dramatically for cows on treatment 3. Insulin concentrations followed the opposite trend. The DMI were positively related to milk yields and negatively related to oxytocin concentrations. Digestibility was negatively related to plasma glucose concentrations in a nonlinear pattern. The possible involvement of hormones in improvement of digestibility is discussed.

Effect of ruminal degradability of crude protein and nonstructural carbohydrates on the efficiency of bacterial crude protein synthesis and amino acid flow to the abomasum of dairy cows.

Four lactating Israeli Holstein cows that were ruminally and abomasally cannulated were used in an experiment with a 4 x 4 Latin square experimental design to study the effects of different amounts of ruminally degradable crude protein (CP) and ruminally degradable nonstructural carbohydrates on ruminal fermentation and efficiency of bacterial CP synthesis. Four diets were formulated to contain the following percentages (percentage of respective fraction) of ruminally degradable protein (RDP) and ruminally degradable nonstructural carbohydrates, respectively: 1) 73.8 and 85.3%, 2) 72.4 and 75.3%, 3) 67.7 and 86.0%, and 4) 66.3 and 76.0%. The 2 x 2 factorial effects of high and low concentrations of RDP or nonstructural carbohydrates were examined. Intakes of DM and organic matter (OM) were similar among treatments, and apparent and true ruminal digestibilities of OM were also similar. Apparent digestibility of CP in the total tract was higher for diets containing high concentrations of ruminally degradable nonstructural carbohydrates. Efficiency of microbial CP synthesis was higher for diets supplemented with low concentrations of RDP and averaged 196 g of microbial CP/kg of OM truly digested in the rumen. Total and bacterial CP flows were higher for diets containing low concentrations of RDP. Therefore, greater amounts of amino acids (AA) of bacterial origin reached the abomasum. The abomasal flow of AA was higher for diets containing low concentrations of RDP. Most of the profiles for essential AA in the abomasum were influenced and balanced by profiles for bacteria. When diets contained a high concentration of RDP (73% of total dietary CP), the supplementation of a high concentration of ruminally degradable nonstructural carbohydrates had no positive influence on bacterial yield or efficiency of bacterial CP synthesis. Other factors, such as AA and peptides included in the RUP fraction, may be important to maximize the efficiency of bacterial CP synthesis.

Increased weight gain and effects on production parameters of Holstein heifer calves that were allowed to suckle from birth to six weeks of age.

Forty Holstein heifer calves were assigned to two treatments. Control calves (n = 20) were fed milk replacer in open buckets, and calves that were allowed to suckle (n = 20) were paired and suckled the same dam three times daily. Treatments were conducted during the first 6 wk following birth; thereafter, all calves received the same management, and weaning was at 60 d of age. During treatment, calves that were allowed to suckle had significantly higher average daily gains than did control calves. However, at 12 wk of age, calves that were allowed to suckle had significantly lower body weights (BW) than did control calves. Age at conception was significantly lower, and BW at conception and conception rate tended to be higher, for calves that were allowed to suckle. Calving age was significantly earlier for heifers that had been allowed to suckle as calves, and BW at calving also tended to be higher. Height at the withers after calving was also significantly higher for those heifers. Milk production during first lactation tended to be higher for the heifers that had been allowed to suckle as calves. Our results indicated that heifer calves that suckled milk during the first 42 d of age had higher average daily gains, higher height at the withers, an earlier age at calving, and a tendency for greater milk production than did calves fed milk replacer.

The effect of abomasal infusion of casein and recombinant somatotropin hormone injection on nitrogen balance and amino acid fluxes in portal-drained viscera and net hepatic and total splanchnic blood in Holstein steers.

Six Holstein steers, 6 mo of age, with a BW range of 180 to 200 kg were used to determine effects of abomasal casein infusion and recombinant bovine somatotropin on amino acid absorption and metabolism in the gut and liver. Catheters were positioned in the hepatic vein, the hepatic portal vein, two mesenteric veins, and a mesenteric artery. Using the same basal diet, treatments consisted of 1) basal diet only (Control), 2) abomasal casein infusion of 300 g/d (Casein), and 3) abomasal casein infusion plus daily injection of 20 mg of bovine somatotropin (ST). All steers were fed the basal diet at a rate of 24 g/kg of BW on a DM basis, in 12 equal meals at 2-h intervals. Initially, Casein and ST treatments were in a balanced cross-over design, and then all steers received the Control treatment. Casein infusion tended to increase BW gain but did not affect BW gain per unit of N intake. The ST treatment increased weight gain (P < .01) and efficiency of dietary DM (P < .01) and N (P < .01) utilization by more than 40% and increased the percentage of absorbed N retained. Nonessential, essential, and total amino acid fluxes in portal-drained viscera (PDV) and their net removal by the liver were not affected by casein infusion. However, ST tended to reduce PDV flux of essential, nonessential, and total amino acids by approximately 30%, and their removal by the liver (P < .08). As a result, ST increased, compared with casein, release of essential (P < .06) and total (P < .10) amino acids from the total splanchnic pool (TSP) into peripheral blood. The ST treatment increased the availability of absorbed amino acids to peripheral tissues, but it did not affect the amino acid profile delivered from splanchnic tissues, especially that of essential amino acids.

Inhibition of lactogenic activities of bovine mammary gland explants by the whey fraction of bovine milk.

The regulation of milk constituents, synthesis and secretion in tissue cultures of the bovine mammary gland was altered by a whey fraction of bovine milk. alpha-Casein gene expression, casein secretion and fatty acid synthesis were inhibited by the whey fraction in a dose-dependent manner. The whey fraction inhibited the enhancement activity of prolactin on alpha-casein gene expression and fatty acid synthesis, and also inhibited casein secretion to the medium, in explants cultured in a medium with or without prolactin. No effect on the expression of the beta-lactoglobulin gene was found.

Effect of the degradation of organic matter and crude protein on ruminal fermentation in dairy cows.

The potential of the dacron bag technique to assess fluctuations in ruminal metabolites was studied using 40 Israeli-Friesian dairy cows assigned to an experiment with a 2 x 2 factorial design. Diets contained a low (62%) or high (65%) percentage of ruminally degradable CP and a low (55%) or high (59%) percentage of ruminally degradable OM. Metabolites were monitored before feeding and at 3 and 6 h postfeeding. Before feeding, total VFA and propionate were higher, and acetate and pH were lower, in diets containing a high percentage of ruminally degradable OM than in diets containing a low percentage of degradable OM. By 3 H postfeeding, acetate, butyrate and pH were lower, and propionate was higher, in the diets containing a high percentage or ruminally degradable OM than in the diets containing a low percentage of ruminally degradable OM. By 6 h postfeeding, propionate was higher, and acetate was lower, in diets containing a high percentage of ruminally degradable OM than in diets containing a low percentage of ruminally degradable OM. In the diets with a high percentage of ruminally degradable OM, before feeding and by 3 h postfeeding, ammonia concentrations were higher and lower, respectively, relative to the diets containing a low percentage of degradable OM. Milk yield and composition and DMI were similar among treatments. The correlation was good between the degradability data obtained by the dacron bag technique and the meal-induced variations in ruminal metabolites. The lack of a positive yield response to controlled fluctuations in ruminal metabolites may be related to surplus CP intake.

Effect of type of protein supplementation on duodenal amino acid flow and absorption in lactating dairy cows.

Four multiparous lactating Holstein cows, fitted with cannulas in the rumen, duodenum, and ileum, were used in a trial with a 4 x 4 Latin square design to examine the effect of source and degradability of dietary CP supplements on AA flow and absorption in the small intestine. The CP supplements consisted of fish meal or meat meal as the animal by-products supplement and soybean meal or heated soybean meal as the plant by-products supplement. Fish meal and heated soybean meal constituted the high RUP diets, and meat meal and soybean meal constituted the low RUP diets. Dry matter intakes were similar among treatments. However, intakes of OM, rumen-degradable OM, total CP, and RDP were affected by the source of the CP supplement and were higher for diets with plant by-products than for those diets with animal by-products. Data were similar for the calculated in situ digestibilities and for true in vivo digestibilities of rumen-degradable OM. Efficiency of bacterial CP synthesis was similar among diets; however, nonbacterial CP flow to the duodenum and OM, CP, and disappearance of AA from the small intestine were affected by the interaction of supplement source and degradability. Heat treatment of soybean meal reduced the availability of most of the essential AA for absorption in the small intestine by 2.3% compared with that of soybean meal; the biggest such reduction (20%) occurred for Met. Availability of AA in the small intestine was affected by source and degradability of the CP dietary supplement. Heat treatment at 140 degrees C for 2.5 h reduced the availability of Met absorption from the small intestine. Although the differences among availabilities of the individual AA in the small intestine ranged from 80 to 84% among treatments, for high yielding cows, these differences may have practical significance.

Relationship between frequent milking or suckling in early lactation and milk production of high producing dairy cows.

Groups of 9 or 10 cows were assigned to one of three treatments 1) machine-milking three times daily, 2) machine-milking six times daily, and 3) suckling three times daily in addition to machine- milking three times daily. Treatments were conducted during the first 6 wk postpartum; thereafter, all cows were milked three times daily. During treatment, milk production was highest for suckled cows and lowest for cows milked three times daily. The DMI were similar for suckled cows and cows milked three times daily but higher for those milked six times daily. Body weight loss was greatest for suckled cows and least for cows milked three times daily. During wk 7 to 18 postpartum, cows milked six times daily exhibited a carry-over effect on milk production that was greater than that of other groups, During treatment, plasma growth hormone and IGF-I concentrations were elevated for suckled cows and, to a lesser extent, for cows milked six times daily. Prolactin and oxytocin similarly increased, but insulin decreased in suckled cows and, to a lesser extent, in cows milked six times daily. Posttreatment differences persisted for insulin and IGF-I, but not for the other hormones. Increased frequency of udder emptying increased milk production, and suckling was superior to machine-milking. High milk production was associated with elevated growth hormone, IGF-I, prolactin, and oxytocin, although cause and effect could not be established. The failure of suckled cows to increase feed intake to match output requires further investigation.

The effect of manipulation in energy allowance during the rearing period of heifers on hormone concentrations and milk production in first lactation cows.

Fifteen Holstein heifers that were 175 +/- 4.0 d old and at BW of 175 +/- 4.9 kg were used to determine the effect of three feeding regimens from 6 to 12 mo of age on growth, blood concentration of several hormones, and milk production during first lactation. The feeding regimens consisted of two periods, the first lasting for 4 mo and the other for the subsequent 2 mo. For group A (restricted) heifers, the diet during period 1 was restricted to 85% of NRC (1988) recommendations (a daily BW gain of .7 kg); during period 2, a high energy, high protein diet was provided for ad libitum intake. Group B (control) heifers received a diet that corresponded to 100 and 90% of the NRC (1988) recommendations in periods 1 and 2, respectively. Group C (ad libitum) intake heifers received a high energy, high protein diet throughout both periods. Daily BW gains of heifers of groups A, B, and C were, respectively, .625, .768, and 1.100 kg for period 1 and 1.162, .705, and .797 kg for period 2. The different feeding regimens influenced the age at which the heifers achieved puberty but did not affect BW at puberty. Milk production during 250 d of lactation was 7056, 6070, and 5975 kg for groups A, B, and C, respectively. A statistical model that included serum derived mitogenic activity and serum prolactin of period 2 accounted for 63% of the difference in milk production at first lactation.