Difference In Daily Milk Yield Research Articles

Effects of grass silage, preserved using formic acid or lactic acid bacteria, on milk production of dairy cows, supplemented with concentrates high or low in metabolizable protein

A continuous production experiment was conducted in Norway with 48 Norwegian Red dairy cows in early- to mid-lactation, to investigate the effect of grass silage with lactic acid bacteria (LAB) or formic acid (FA) additives, on milk yield (MY) and milk protein yield (MPY). Grass wilted to 250 g dry matter (DM)/kg was inoculated with homofermentative LAB to obtain LAB silage, whilst FA silage was produced adding a FA-based additive. The two silages were fed ad libitum and supplemented with an average 10.3 kg of either high (H) or low (L) metabolizable protein (MP) concentrates, in a 2 ✗ 2 factorial arrangement of treatments. The treatments were LAB silage and L concentrate, LAB silage and H concentrate, FA silage and L concentrate and FA silage and H concentrate. The use of FA resulted in lower levels of residual water-soluble carbohydrates (WSC), and higher levels of ammonia nitrogen (NH3N), compared to LAB. In situ results for FA silage showed lower rumen degradability of crude protein (CP), while gas in vitro results showed lower utilizable CP (uCP), compared to LAB silage (782 vs. 750 g/kg DM and 128 vs. 119 g/kg DM, respectively). The purine over creatinine (PDC) index did not indicate any effects on the microbial protein synthesis (MPS) from any of the treatments. The higher daily intake of FA silage (12.5 vs.13.7 kg DM for LAB and FA, respectively, P < 0.001), did not result in significant differences in daily MY (31.0 vs. 30.2 kg, P = 0.208), nor MPY (1.08 vs.1.07 kg/day, P = 0.878) for LAB and FA, respectively. Feeding H concentrate gave higher MPY (P = 0.036), higher urea in milk (P < 0.001), plasma (P < 0.001) and urine (P = 0.008) and tended to give higher MY (P = 0.063) for both silages. For amino acids (AA) in plasma, alanine was higher for FA silage than for LAB silage (P = 0.030), while histidine (P = 0.001), leucine (P = 0.015) and glutamine (P = 0.007) were higher for both silages when cows were fed H concentrate. In conclusion, the FA and LAB additives did not affect MY or MPY any differently. Feeding H concentrate resulted in higher MPY for both silages, but reduced nitrogen (N) efficiency.

Relationship of GHRL Gene Polymorphism with Milk Production and Components in Holstein Cows

The current study was conducted in private station located in the middle of Iraq by using 100 samples of blood to determine the effect of GHRL gene polymorphism on milk traits in Holstein cows. Results showed two alleles with co-dominance and three genotypes was detected in the site -97, the allele frequency was 0.72 and 0.28 for G and A allele respectively. Results showed a significant effect of SNP on lactation period length (P<0.01). The cows with mutant genotype (AA) were the longest lactation period (241 day) while the cows with wild genotype were the shortest lactation period. Total milk yield affected significantly (P<0.01) by allele type, the highest quantity of milk yield was in cows with mutant genotype namely, 3366.77 Kg. High significant differences in daily milk yield were reported in cows according the alleles type, AA cows genotypes achieved 13.97 Kg /day compared with the cows with GG genotype which achieved 8.82 kg/day. Milk components such as lactose and protein were affected significantly (P<0.01) by GHRL gene SNP, the highest rate of lactose and protein were noticed in cows with wild genotype namely, 5.45 and 3.60% respectively. Milk fat differed significantly (P<0.05) in cows depending on its genotype, the highest rate was recorded in cows with wild genotype (GG) namely 3.90%.

Comparative Assessment of the Stress Response of Cattle to Common Dairy Management Practices.

While studies have been conducted examining the stress response of dairy cattle to individual acute and chronic stressors, the results are difficult to compare due to differences in study design and analysis methods. The aim of the present study was to conduct a comparative assessment of the impact of eight common stimuli: artificial insemination (AI), embryo transfer (ET), morning milking (MM), evening milking (EM), veterinary examination (VE), ultrasound examination (US), hoof trimming (HT), and natural breeding (NB) on the hypothalamic-pituitary-adrenal axis and milk production of 24 Holstein-Friesian cattle. After random allocation into control and treatment groups, a total of five blood samples were collected 40 min (Ba1) and 20 min (Ba2) prior to stimulus application, immediately following the stimulus (St), as well as 20 min (Re1) and 40 min (Re2) post-stimulus. A comparison between the overall serum cortisol concentrations in the treatment groups showed a significant difference between HT to AI (p = 0.006), ET (p = 0.010), MM (p = 0.021), VE (p = 0.009), EM (p = 0.007), and US (p = 0.010), except for NB (p = 0.542). There is no significant difference between the control groups (p > 0.05). The stimuli HT (p < 0.001) and NB (p < 0.001) showed significant increases in cortisol following stimulus application, and the levels failed to decrease significantly by sample Re2. No significant differences in daily milk yield (kg) were measured amongst the tested stimuli (p = 0.472) nor amongst the groups 'Control', 'Treatment' and 'no stimulus' (p = 0.350). In conclusion, when factors such as increased physical activity, novel social interaction, sexual arousal, and a more intense restriction of movement are present, the animal's perceived controllability and predictability might decrease, affecting the animal's response to stress. Treatments carried out while animals are restrained in a headlock while remaining within their regular group likely result in a less intense activation of the HPA axis.

Strong evidence for association between K232A polymorphism of the DGAT1 gene and milk fat and protein contents: A meta-analysis

The relationship between K232A polymorphism of the DGAT1 gene and milk yield and composition was evaluated by meta-analysis of pooled data of more than 10,000 genotyped cattle. Four genetic models, including dominant (AA+KA vs. KK), recessive (AA vs. KA+KK), additive (AA vs. KK), and co-dominant (AA+KK vs. KA) were used to analyze the data. The standardized mean difference (SMD) was used to measure the size of the effects of the A and K alleles of K232A polymorphism on milk-related traits. The results showed that additive model was the best model for describing the effects of K232A polymorphism on studied traits. Under additive model, milk fat content was strongly decreased in cows having the AA genotype (SMD = -1.320). Furthermore, the AA genotype reduced the protein content of milk (SMD = -0.400). A significant difference in daily milk yield (SMD = 0.225) and lactation yield (SMD = 0.697) was found between cows carrying AA and KK genotypes, suggesting the positive effects of the K allele on these traits. Cook's distance measurement suggested some studies as outliers and sensitivity analyses by removing influential studies revealed that the results of meta-analyses for daily milk yield, fat content and protein content were not sensitive to outliers. However, the outcome of the meta-analysis for lactation yield was strongly influenced by outlier studies. Egger's test and Begg's funnel plots showed no evidence of publication bias in included studies. In conclusion, the K allele of K232A polymorphism showed a tremendous effect on increasing fat and protein contents in the milk of cattle, especially when 2 copies of this allele are inherited together, whereas the A allele of K232A polymorphism had negative effects on these traits.

Improving parlor efficiency in block calving pasture-based dairy systems through the application of a fixed milking time determined by daily milk yield and milking frequency

Adjusting end-of-milking criteria, in particular applying a maximum milking time determined by expected milk yield at an individual milking session, is one strategy to optimize parlor efficiency. However, this strategy can be difficult to apply practically on farm due to large differences in session milk yield, driven by milking interval, which affects milking routines and can be limited by in-parlor technology. The objective of this study was to test the hypothesis that a single fixed milking time (duration) could be applied at all milking sessions without compromising milk production or udder health for a range of milking intervals. To test the hypothesis, 4 experimental herds were established: (1) herd milked twice a day (TAD) using a 10- and 14-h interval, (2) herd milked TAD using an 8- and 16-h interval, (3) herd milked 3 times in 2 d using a 10-19-19-h interval, and (4) herd milked once a day (OAD). Herds consisted of 40 cows each, and were established for two 6-wk experimental periods, one in peak lactation and the other in mid-late lactation. Within each herd, half the cows had an end-of-milking criterion of 0.35 kg/min (Flow), and the other half had milking ended after a fixed period of time (FixedT) based on the average milking session yield, the daily milk yield divided by average number of milkings per day, irrespective of milking interval. We found no differences in daily milk yield between end-of-milking criteria due to residual milk from one milking likely increasing the proportion of milk in the udder cistern at the next milking session for the FixedT treatment. However, fat yield was compromised when the percentage of the herd with a truncated milking exceeded an estimated 33% at a milking session, which occurred in the TAD 8-16 herd due to the divergence from the average milking interval (in the case of TAD, 12-12 h). Applying a fixed milking time had no detrimental effects on udder health, except in the OAD herd in mid-late lactation, which had both a higher cell count and new intramammary infection rate. This warrants further investigation, although the majority of cultured bacteria were coagulase-negative staphylococci (CNS). Consequently, we conclude that, in general, with appropriate monitoring (e.g., weekly inspection) to ensure the proportion of the herd with truncated milkings does not exceed 33%, farmers in pasture-based dairy systems can use a fixed milking time to improve parlor efficiency.

Serum and Hair Trace Element and Mineral Levels in Dairy Cows in Relation to Daily Milk Yield.

The objective of the present study was to assess hair and serum trace element and mineral levels in dairy cows in relation to daily milk yield. A total of 70 healthy 5-6-year-old Simmental cows were divided into two groups (n = 35) with high and low daily milk yield using median as a cut-off value. Hair and serum trace element and mineral content was evaluated using inductively coupled plasma mass-spectrometry. A nearly twofold difference in daily milk yield (43.8 ± 9.7 vs 21.3 ± 7.1 L/day, p < 0.001) was significantly associated with 11% lower hair Cu (p = 0.043) and 35% higher Se levels (p = 0.058) content when compared animals with lower daily milk yield. Serum trace element levels were found to be more tightly associated with milk productivity in dairy cows. Particularly, serum levels of Se and Zn were found to be 73 and 35% higher in cows with higher milk productivity in comparison to animals with lower milk production, respectively. Serum Co levels also tended to increase with higher milk productivity. Serum minerals including Ca, Mg, and P were also found to be higher in highly productive cows by 6%, 14%, and 71%, respectively. The overall regression model based on serum trace element and mineral levels accounted for 38% of daily milk production variability. Generally, improvement of essential trace element and mineral supply, as well as prevention of copper overload in dairy cows, may be considered the potential tool for modulation of milk productivity.

Milk yield and rectal temperature in West African Dwarf goats as affected by wattle and litter size

This study was conducted to investigate milk yield and rectal temperature in West African Dwarf (WAD) goats as affected by wattle and litter size. A total of 28 lactating does were used for the experiment. 13 does had wattle (bilateral) while 15 had no wattle. 14 does had twin birth while the other 14 had single birth. The goats were fed at 5% body weight with combination of concentrate and grass (Panicum maximum and Pennisetum purpureum) in ratio 50:50 twice per day in the morning and evening (zero grazing). The lactating does were hand milked once per day (08.00) and thrice per week for the period of 12 weeks. The goats were housed in cross ventilated pens with slatted floor. Rectal temperature was taken after milking of each animals using digital thermometer. Data collected were analysed using SAS (2010) in a randomized complete block design. The results showed that wattle and litter size had significant effect on milk yield and rectal temperature in WAD goats. Wattled animals produce significantly (P&lt;0.05) higher milk yield of 297.72 g/day compared to their non wattled counterparts (255.11 g/day). Animals with wattle however had higher rectal temperature of 39.35°C compared to animals without wattle (39.23°C). Also twin littered does produced daily milk milk yield of 292.74 g/day significantly (P&lt;0.05) higher than single littered counterparts (257.04 g/day). The interaction between wattle and litter size showed that there was no significant difference in daily milk yield in wattled animals regardless of the litter size. However, in non-wattle animals, does with twin birth produced daily milk yield of 283 g/day significantly (P&lt;0.05) higher than 235 g/day for does with single birth. Also, wattled does with single birth had significantly (P&lt;0.05) higher rectal temperature of 39.43°C when compared with wattled does with twin birth. However, in non wattle animals, does with single birth had significantly lower rectal temperature of 39.18°C as compared with does with twin birth (39.29°C). It was concluded that WAD goats with wattle and twin birth produces more milk than those without wattle and single birth. Therefore, WAD goats with wattle should be selected for lactation purpose especially those with twin birth.

Rumen metabolism, omasal flow of nutrients, and microbial dynamics in lactating dairy cows fed fresh perennial ryegrass (Lolium perenne L.) not supplemented or supplemented with rolled barley grain

The objective of this study was to evaluate the effect of rolled barley grain (RB) supplementation on rumen metabolism, omasal flow of nutrients, and microbial dynamics in lactating dairy cows fed fresh perennial ryegrass (Lolium perenne L.; PRG)-based diets. Ten ruminally cannulated Holstein cows averaging (mean ± standard deviation) 49 ± 23 d in milk and 513 ± 36 kg of body weight were assigned to 1 of 2 treatments in a switchback design. The treatment diets were PRG only (G) or PRG plus 3.5 kg of dry matter RB (G+RB). The study consisted of three 29-d periods where each period consisted of 21 d of diet adaptation and 8 d of data and sample collection. A double marker system was used to quantify nutrient flow entering the omasal canal along with labeled 15N-ammonium sulfate to measure bacterial, protozoal, and nonmicrobial N flow. Rumen evacuation techniques were used to determine nutrient and microbial pool size, allowing the calculation of fractional rates of digestion and microbial growth. There was no difference in daily milk yield or energy-corrected milk yield between treatments. Milk fat concentration and milk urea N decreased, whereas milk protein concentration increased in cows fed the G+RB diet. During the omasal sampling phase, dry matter intake was higher in cows fed the G+RB diet. Ruminal and total-tract neutral detergent fiber digestibility was lower in G+RB cows; however, no difference was observed in reticulorumen pH. The rumen pool size of fermentable carbohydrate was increased in cows fed the G+RB diet; however, the fractional rate of digestion was decreased. Flow of nonammonia N and bacterial N at the omasal canal increased in cows fed the G+RB diet compared with the G diet. Protozoa N flow was not different between diets; however, protozoa appeared to supply a much larger amount of microbial N and exhibited shorter generation time than previously considered. Feed N ruminal digestibility, corrected for microbial contribution, was similar for both treatments (88.4 and 89.0% for G and G+RB, respectively). In conclusion, RB supplementation did not benefit overall animal performance; however, it reduced ruminal neutral detergent fiber digestibility and increased bacterial N flow. The results demonstrate the large dependence of cows consuming PRG-based diets on microbial N as the main source of nonammonia N supply. Additional quantitative research is required to further describe the supply of nutrients and microbial dynamics in cows consuming PRG-based diets in an effort to determine most limiting nutrients.

Morning and evening pasture access – comparing the effect of production pasture and exercise pasture on milk production and cow behaviour in an automatic milking system

Although pasture is low-cost feed, many farmers find it difficult to maintain high milk yield when using pasture for high-yielding dairy cows in automatically milked herds. Therefore, a seven-week experiment with 40 cows in early to mid-lactation was performed to evaluate a management model for including pasture in the diet without jeopardizing milk production. Within a part-time grazing system with morning and evening outdoor access, we compared a group with ad libitum grass silage indoors combined with access to a small grass-covered permanent paddock for exercise and recreation (group EX) with a group offered production pasture at a high allowance per cow and day combined with restricted grass silage allowance at night (group PROD). Both groups had the same outdoor access times and the same concentrate allowance based on pre-experimental milk yield. Milk yield and milking frequency were recorded daily in the automatic milking unit. Milk recordings and samplings for determination of milk composition took place weekly and outdoor behaviour of cows was recorded during pasture access hours on six observation days, evenly distributed over the experimental period. During the experiment, average metabolisable energy concentration was higher in the grass silage offered both groups than in pasture herbage. However, our results showed no significant difference in daily milk yield between treatments. Furthermore, no significant differences between treatments were found in energy-corrected milk, milk fat production, or body weight change. Milk protein production was, however, significantly higher in group PROD. In early lactation, no difference in milking frequency was observed between treatments while for cows in mid- to late lactation, milking frequency was significantly higher in group EX than group PROD. Over the entire experiment, group EX cows spent significantly less time outdoors than group PROD. In conclusion, offering high yielding dairy cows in automatic milking systems high-quality pasture at a high allowance for a few hours in morning and afternoon appears to be an interesting alternative to exercise paddock with full indoor feeding, as it can reduce costs for supplementary silage, facilitate natural behaviour, and encourage cows to spend more time outdoors, while maintaining milk production at a level comparable to that of full indoor feeding.

Association of lameness with milk yield and lactation curves in Chios dairy ewes.

The objective of the study was twofold: (i) to quantify the differences in daily milk yield (DMY) and total milk yield (TMY) between lame and non-lame dairy ewes and (ii) to determine the shape of lactation curves around the lameness incident. The overall study was a prospective study of lameness for the surveyed sheep population, with a nested study including the selection of matching controls for each lame ewe separately. Two intensively reared flocks of purebred Chios ewes and a total of 283 ewes were used. Data, including gait assessment and DMY records, were collected on a weekly basis during on-farm visits across the milking period. A general linear model was developed for the calculation of lactation curves of lame and non-lame ewes, whereas one-way ANOVA was used for the comparisons between lame ewes and their controls. Lameness incidence was 12.4 and 16.8% on Farms A and B, respectively. Average DMY in lame ewes was significantly lower (213.8 g, P < 0.001) compared with the rest of the flock, where DMY averaged 1.340 g. The highest DMY reduction in lame ewes was observed during the week 16 of the milking period (P < 0.001), whereas the reduction of DMY, for lame ewes, remained significant at P < 0.001 level from week 8 to week 28 of milking. Comparisons between lame and controls revealed that at the week of lameness diagnosis a significant DMY reduction (P ≤ 0.001) was observed in lame ewes (about 32.5%), which was maximised 1 week later (35.8%, P ≤ 0.001) and continued for several weeks after recovery, resulting in 19.3% lower TMY for lame ewes for the first 210 d of the milking period (P < 0.01). Moreover, at flock level, TMY for non-lame and lame ewes, as calculated by the general linear model, was 318.9 and 268.0 kg, respectively. The results of this study demonstrate evidence of significant financial losses in dairy sheep due to lameness which, however, need to be accurately estimated in further, more detailed, analyses.

Evaluation of Udder Cisterns and Effects on Milk Yield of Dairy Ewes

Nine Manchega (0.94 L/d) and 10 Lacaune (2.07 L/d) ewes at the same stage of lactation (90 d in milk) were used to study the interbreed differences in milk yield, mammary morphological traits, and machine-milking ability. Udder traits were measured after 6h of udder filling before the start of the experiment. Cisternal area (by ultrasonography), cisternal milk (by teat cannula drainage), and alveolar milk (by machine milking after an intravenous oxytocin injection) were randomly measured 8h after milking for 2 wk consecutively either with an intravenous injection of an oxytocin receptor blocking agent (atosiban, AT) or without (control, C) to avoid the occurrence of milk letdown before milking. Lacaune ewes had greater udder depth (22.5±0.9 vs. 19.6±0.9cm) and cistern height (27.1±3.8 vs. 15.6±3.5mm), whereas Manchega ewes had longer (42.7±1.5 vs. 32.7±1.5mm) and wider teats (17.4±0.5 vs. 13.9±0.5mm). Values per half udder for Manchega and Lacaune ewes differed in cisternal area (12.8±0.7 and 23.7±0.6cm2) and cisternal milk (120±0.6 and 269±0.5mL), but not in alveolar milk (95±0.5 and 102±0.4mL), respectively. Cisternal area and cisternal milk were positively correlated (r=0.79). Ratios between cisternal and alveolar milk were 56:44 and 73:27 for Manchega and Lacaune ewes, respectively. Cisternal milk volumes obtained with the AT or C treatment were similar in Manchega (111±10 vs. 122±8mL) but differed in Lacaune ewes (239±8 vs. 299±8mL), respectively. Consequently, alveolar milk with AT vs. C was similar in Manchega (104±8 vs. 86±7mL) but different in Lacaune ewes (115±7 vs. 89±7mL). Results of this experiment confirm the need for the use of an oxytocin-blocking agent for accurate evaluation of milk contained in the udder of dairy ewes. Moreover, despite the differences in daily milk yield, alveolar milk did not vary between breeds, emphasizing the role of the cisternal more than the alveolar compartment for maximizing daily milk secretion in dairy sheep.

Omitting the Dry-Off Period Negatively Affects Colostrum and Milk Yield in Dairy Goats

Seventeen pregnant multiparous Murciano-Granadina dairy goats, kept in a semi-intensive exploitation system with once daily milking throughout lactation and 1 kidding per year (milk yield, 577 L/300 d), were used to study the effects of dry-off period length on performance during the subsequent lactation. Goats were mated at wk 29 of lactation and were assigned to 2 experimental groups according to dry-off treatment: goats that were dried off 56 d before expected kidding (D56; n=9) and goats without dry-off (D0; n=8). After parturition, kids were removed from their mothers and weighed before suckling. Goats were hand milked to obtain colostrum and were machine milked thereafter. Colostrum was sampled for composition and IgG analysis. Milk yield was recorded weekly during the preceding and subsequent lactations. Udders were biopsied in a sample of goats at d −65 (late lactation), d −49 (during dry-off), and d 48 (early lactation) to kidding (d 0). Apoptotic and proliferating cells in mammary tissues were detected immunohistochemically. Five goats (63%) in the D0 group dried off spontaneously at 27±4 d before kidding and were considered separately (D27). The rest of the D0 goats yielded 0.86 L/d from d −56 to kidding. Goats kidded 2.25 kids/goat, but the D0 kids had smaller birth weights (1.7kg) than the D27 (2.2kg) and D56 (2.1kg) kids. Colostrum of the D0 goats contained less IgG (5.6mg/mL) than the D27 (32.9mg/mL) and the D56 (42.4mg/mL) goats. In the subsequent lactation (210 d), the D0 goats produced less milk (1.78 L/d) than the D27 (2.51 L/d) and D56 (2.24 L/d) goats, with no detectable difference between the D27 and D56 goats. Apoptosis and proliferation indices increased from 0.51 and 2.09%, at d −65, to 1.75 and 7.12% at d −49 (d 7 of dry-off) in D56 goats. Despite differences in daily milk yield during early lactation (d 48) between the D0, D27, and D56 treatments (1.73, 2.68, and 2.53 L/d, respectively), no differences in apoptosis or proliferation indices were detected (D0: 0.65 and 2.48%; D27: 0.68 and 1.37%; and D56: 0.71 and 2.95%), indicating that duration of the dry period did not affect mammary cell turnover during the subsequent lactation. Omitting the dry period between lactations reduced the quality of colostrum and had negative effects on milk yield in dairy goats. Goats dried off spontaneously for 27 d were as productive as goats dried off for 56 d, indicating that less than 2 mo of dry-off may be sufficient in practice.

The effect of pre-milking teat-brushing on milk processing time in an automated milking system

Cow throughput in an automatic milking system (AMS) is limited by system parameters such as the time required for pre-milking udder preparation and cup attachment, physiological responses of the cow (such as milk let-down and milking-out rate), milking machine features and cow behaviour. A single-factor cross-over design was used to investigate the effect of pre-milking teat brushing on milk processing time in an AMS operating in an extensive grazing farming system. Teat brushing consisted of two roller brushes tracking up each teat three times (total brushing time of up to 45 s/cow). Cows were allocated to one of two treatment groups with either no brushing (NB) or brushing (B) for a 4-week period before being changed to the other treatment. Teat brushing resulted in shorter average cups-on-time (B = 506.1 s, NB = 541.0 s, P = 0.0001), longer average milk processing time (B = 10.30 min, NB = 9.76 min, P = 0.001) and no difference in daily milk yield (B = 14.67, NB = 14.71 kg/cow, P = 0.826). There was no difference between the two treatments in the success of cup attachment (B = 3.76%, NB = 5.10% unsuccessful milking attempts, P = 0.285). The estimated time cost of pre-milking teat brushing was 53 min for every 100 milkings, equivalent to an additional 5-6 milkings for every 100 milkings by an AMS. The importance of these potential time savings is discussed in relation to automatic milking in farming systems that aim for a lower per cow milking frequency and high ratio of cows to AMS.

Reproductive Performance and Milk Production of Assaf Sheep in an Intensive Management System

The Assaf breed of dairy sheep, a stabilized cross of the Awassi and East Friesian breeds, has replaced the Awassi as the breed of choice in its country of origin, Israel, and has spread to other Mediterranean countries. In Israel the Assaf breed is managed under an intensive production system involving weaning lambs at birth, rearing them artificially, and milking ewes after parturition. There are several breeding periods in the year when ewes are mated following hormonally synchronized estrus. Records of 18,976 lactations from 5 farms were analyzed to investigate factors that influenced Assaf milk and reproductive performance. Lactation curves were fitted to each lactation, and a range of parameters and calculated values were analyzed. Daily milk yield records also were analyzed to describe a typical Assaf lactation and compared with those of the Awassi breed. Factors affecting age at first lambing also were studied. An average Assaf ewe kept under this intensive management regimen was found to produce 334L of milk during a 173-d lactation. Mean litter size was 1.57 lambs/ewe lambing, and lambing interval was 272 d. Milk production was affected by litter size, with twin- and triplet-bearing ewes producing approximately 20L more milk per lactation than single-bearing ewes. Day length was the major environmental variable influencing milk yield. The difference between midsummer and midwinter day lengths accounted for a difference in daily milk yield of 0.44L in favor of summer. Ewe lambs that were mated for the first time at later ages produced more lambs and more milk due to greater early lactation characteristics. Milk production was found to be negatively associated with subsequent reproductive performance. Comparing these results with those from an earlier study in the Awassi breed, the Assaf was found to produce less milk during a shorter lactation than the Awassi, but its greater litter size made it a more profitable breed.

Protective Effect of Staphylococcus chromogenes Infection Against Staphylococcus aureus Infection in the Lactating Bovine Mammary Gland

The susceptibility of uninfected or Staphylococcus chromogenes-infected quarters to challenge with Staphylococcus aureus was measured. Seventeen S. chromogenes -infected quarters were challenged by infusion of S. aureus into the teat sinus; 47% (8 of 17) became infected and all 18 uninfected quarters challenged similarly with S. aureus became infected. No differences in daily milk yield were seen between uninfected quarters and S. chromogenes-infected quarters prior to S. aureus infusion. Postinfusion, milk yield for S. aureus-infected, S. chromogenes-infected, and S. chromogenes- and S. aureus-infected quarters differed.Somatic cell counts were elevated in S. chromogenes-infected quarters compared with uninfected quarters prior to S. aureus infusion. Somatic cell counts were not different between S. aureus- and S. chromogenes- and S. aureus-infected quarters postinfusion, but were different for S. chromogenes-infected quarters. Chloride concentrations in S. chromogenes-and S. aureus-infected quarters were different from either S. aureus-infected or S. chromogenes-infected quarters. Staphylococcus aureus colony forming units in quarters with preexisting S. chromogenes infections were lower than S. aureus colony-forming units in previously uninfected quarters. Possible protective mechanisms induced by S. chromogenes against superinfection by S. aureus are discussed.

Milk yield responses by dairy cows in mid-lactation to changes in feeding levels

The reduction in milk production following a decrease in feeding level was compared with the increase in milk following an increase in feeding level of cows. Forty cows in their 5th month of lactation were allocated to 2 groups and offered either ad libitum pasture or restricted in their grazing so that, after 32 days, the difference in daily milk yield between the groups averaged 3 L/cow. Cows in each group were then offered cut pasture in stalls for 4 weeks to obtain mean daily intakes of either 14.4 or 10.2 kg DM/ cow The reduction in yield of milk energy (0.133 MJ/MJ metabolisable energy intake) following the decrease of intake from 14.4 to 10.2 kg DM/cow.day was similar to the increase in yield of milk energy (0.140 MJ/MJ metabolisable energy intake) following an increase in intake from 10.2 to 14.4 kg DM/cow.day. We conclude that, for cows in mid-lactation, the decrease in milk production following a decrease in feeding level is similar to the increase in milk production following an increase in feeding level. This implies that increases in milk production due to increased feeding can be predicted from experiments which measured reductions in milk production.

Effects of double suckling at pasture 1. Cow performance

ABSTRACTTwo experiments were conducted to compare the effects of single and double suckling on the performance of Hereford × Friesian and Friesian cows at pasture. Double-suckled cows each fostered a Friesian male calf in addition to their own calf. Cows were housed from calving to turnout for 57 and 35 days in experiments 1 and 2 respectively, with corresponding grazing seasons lasting 152 and 146 days. During the grazing season the two suckling treatments were stocked on a series of adjacent plots of equal area, with the occupancy of each plot pair being reversed daily. Live weights, milk yields, herbage intakes, and daylight grazing times and nursing activities were recorded on three occasions 28 days apart.Double-suckled cows lost significantly more weight than single-suckled cows from calving to turnout in both experiments (39·5 v. 3·3 kg and 45·7 v. 20·6 kg), gained more weight from turnout to weaning in experiment 1 (58·4 v. 23·3 kg) but gained less in experiment 2 (17·5 v. 32·3 kg). Double-suckled cows produced significantly more milk than single-suckled cows: 10·1 v. 8·3 and 13·5 v. 9 1 kg/day in experiments 1 and 2 respectively. Differences in daily milk yield in experiment 2 were apparent 28 days after calving.Suckling treatments did not influence herbage intakes or daylight grazing times and nursing frequencies. Mean nursing intensities were 1·0 calves per single-suckled cow, compared with 1·8 calves (experiment 1) and 2·2 calves (experiment 2) per double-suckled cow. Double-suckled cows nursed significantly more ‘foreign’ calves than single-suckled cows. Total calf weight at weaning from double-suckled cows in experiments 1 and 2 was respectively 364·6 and 344·4 kg, which was 1·64 of the corresponding weights weaned by single-suckled cows (221·1 and 209·4 kg).

The influence of dietary protein intake during lactation on the reproductive performance of sows

SUMMARY1. Forty-five Large White gilts were given 2·20 kg daily of a diet containing 14·0% crude protein during three successive pregnancies. During a 6-week lactation they received 5·30 kg daily of one of three diets containing 19·0% (HP), 16·5% (MP) or 14·0% (LP) crude protein.2. Daily milk yield was estimated on the 10th, 20th, 30th and 40th day of lactation. Milk samples were obtained from the same sows for the determination of protein, fat, lactose and total solids on the 11th, 21st, 31st and 41st day.3. One sow and litter from each treatment in each lactation was placed in metabolism cages during lactation and estimates of nitrogen and dry matter excretion obtained.4. As the concentration of protein in the diet decreased the average 42-day gain in litter weight from birth increased significantly in the first lactation. This trend continued in the second lactation although it was not significant but did not appear in the third.5. There was no marked difference in daily milk yield between treatment groups.6. There was a significantly greater loss of live weight by the sows on the lower levels of protein in the first lactation. These differences were not significant in the second and third lactations.

Sample Size for Experiments on Milk Yield

Graphs are presented that will permit dairy researchers to estimate the number of cows required to have 50 or 80% chance of detecting specified differences in true mean milk yield between two or more treatment groups. Relatively small experiments are shown to be almost hopelessly insensitive unless experimental errors can be reduced below levels ordinarily encountered. If an experimenter has available fewer than ten cows per treatment, estimates show he has less than a 50% chance of detecting a true mean difference in daily milk yield of 4kg in a completely randomized experiment, 3.5kg with a covariance analysis, 3.2kg in a randomized block design, or 1.2kg in a crossover trial.

The effect of feed supplements on the yield and composition of milk from cows grazing good pasture

SummaryTwo experiments are described in which spring-calved Ayrshire cows were fed supplementary food when grazing good, leafy pasture.In the first experiment 6 lb of a mixture of three parts bruised oats and one part flaked maize was fed daily to three groups of five cows. One group received the supplement from 1 July until 30 October, and the other two groups from 1 August and 1 September respectively. A control group received no supplement.In no month was there any statistical difference in daily milk yield between supplemented and unsupplemented groups of cows. The group fed from 1 July gave the highest total milk yield in the period June to October, but with a return of only 1 gal of milk from 34 lb of meal.The length of the lactation was not significantly affected by the treatment.In the second experiment, three groups of four cows on a 9-week change-over trial (4 May-5 July) grazed herbage containing an average of only 17·6% dry matter and 3·8% crude fibre. On the three treatments the cows ate pasture only, pasture plus 1·6 lb hay/day and pasture plus 5·7 lb of meal/day. The meal consisted of four parts by weight of undecorticated cotton cake, four of bruised oats and three of locust beans.Milk yield was significantly increased from 41·8 lb on the all-grass ration to 43·2 lb/day on the meal treatment but the hay did not affect milk yield.The fat content of the milk was significantly increased from 3·77 to 3·91% on the hay treatment, whereas the solids-not-fat content of the milk was not significantly affected by any of the treatments.At the present-day prices of the feeds and with cows on good leafy pasture it was clearly uneconomic to feed the meal supplements.