Decline In Milk Yield Research Articles

A practical future-scenarios selection tool to breed for heat tolerance in Australian dairy cattle

Climate change will have an impact on dairy cow performance. When heat stressed, animals consume less feed, followed by a decline in milk yield. Previously, we have found that there is genetic variation in this decline. Selection for increased milk production, a major breeding objective, is expected to reduce heat tolerance (HT), as these traits are genetically unfavourably correlated. We aimed to develop a future-scenarios selection tool to assist farmers in making selection decisions, that combines the current national dairy selection index, known as the balanced performance index (BPI), with a proposed HT genomic estimated breeding value (GEBV). Heat-tolerance GEBV was estimated for 12 062 genotyped cows and 10 981 bulls, using an established genomic-prediction equation. Publicly available future daily average temperature and humidity data were used to estimate mean daily temperature–humidity index for each dairy herd. An economic estimate of an individual cow’s heat-tolerance breeding value (BV_HT) was calculated by multiplying head-tolerance GEBVs for milk, fat and protein by their respective economic values that are already used in the BPI. This was scaled for each region by multiplying BV_HT by the heat load, which is the temperature–humidity index units exceeding the threshold per year at a particular location. BV_HT were incorporated into the BPI as: BPI_HT = BPI + BV_HT; where BPI_HT is the ‘augmented BPI’ breeding value including HT. A web-based application was developed enabling farmers to predict the future heat load of a herd and take steps to aim at genetic improvement in future generations by selecting bulls and cows that rank high for the ‘augmented BPI’.

Cross-breeding in Cattle for Milk Production: Achievements, Challenges and Opportunities in India-A Review

This paper reviews experiences with cross-breeding for milk production in India. Data were compiled from different studies evaluating the performance of different grades of cross-bred animals as well as local breeds. Relative performance of indigenous breeds compared with different grades of cross-breeds was calculated. Traits considered were milk yield per lactation, age at first calving, services per conception, lifetime milk yield and total number of lactations completed. Exotic inheritance of around 50% is the most ideal for growth, reproduction and milk production, and the yield in higher crosses falls short of theoretical expectations. The grading up, therefore, to a total replacement of genes will not lead to higher production in cattle. The crosses of temperate with improved indigenous breeds (Sahiwal, Red Sindhi, Gir, Tharparkar) attained the same level of performance under uniform feeding and are superior to crosses from other native cattle. Holstein crosses were superior to other temperate breed crosses for growth and production while Jersey crosses have better reproductive efficiency. Decline in milk yield from F1 to F2 generations on account of inter se mating among F1 crossbreds is small. The Friesian crossbreds excelled in milk yield, but were slightly older at first calving and had slightly longer calving intervals than Jersey crosses. A serious decline in performance from F1 to F2 was observed in both crosses: F2 were about eight months older at first calving and produced about 30% less milk. They had also much longer calving intervals. The combination of ART with advanced molecular genetics plus the availability of simple recording schemes provide great opportunities for developing and multiplying synthetic breeds at a much faster rate than in previously conducted breeding programmes. Although cross-breeding faces a number of challenges such as better infrastructure, higher demand for health care, there are many advantages of using it. These are higher production per animal, higher income for the families and provision of high-value food. It is therefore likely to continue to be an important livestock improvement tool in the tropics in the future, where farmers can provide sufficient management for maintaining animals with higher input requirements and access to the milk market can be secured.

Effect of Clinical Ketosis on Milk Yield in Mehsana Buffaloes

A study was conducted to assess the factors influencing the economic losses due to ketosis by gathering data from samples of eighteen ketotic Mehsana buffaloes. The study outlines the effect of ketosis in eighteen buffaloes. Three (16.67%) of 18 ketotic buffaloes showed 20-30 percent drop in milk yield, whereas 40-50 per cent drop in production was exhibited by 7 (38.89%) buffaloes. The average drop in daily milk yield was recorded to be 3.40+0.27 liters (34.24%) and the recovery after treatment could restore only 22.52 per cent (3.24+026 liters) milk per day. Decline in milk yield from 25.92 percent in 0 to 1 month of lactation to 40.72 percent at 3-4 month postpartum with an increasing trend.

Influence of stage of lactation on quantitative and qualitative milk production parameters in goats

Goat lactation is synonymous to an agricultural production function with three distinct production regions namely: early, mid and late lactation. It is characterised by an increase in milk yield in early lactation to a possible peak in the mid lactation and then a decline in milk yield as it reaches the end of lactation. However, the other milk constituencies (protein, fat, lactose, etc ) do not follow the same trend as total milk yield through the 3 lactation stages. Therefore, it is suffice to suggest that the understanding of the physiological changes in these stages of lactation is crucial in maximizing milk production in goats. The present discussion explores the importance of different stages of lactation in milk production in influencing yield and milk composition. Milk yield and its composition are influenced by various factors, among these stage of lactation is very significant. The proportion of protein, lactose, fat and total solids declined slightly with advance in lactation and a steady fall in milk yield. This is on the basis that milk yield is a function of the number of mammary secretory cells and their metabolic activity change during the course of lactation. The significant stage of lactation effect in most studies may have practical implications in determining optimal feeding management to maximize total lactation yield and milk composition. Therefore, the knowledge of physiological activities during different stages of lactation is critical to dairy animal nutrition and management decision support systems for optimization of goat dairy flock production processes.

Effects of feeding lutein on production performance, antioxidative status, and milk quality of high-yielding dairy cows

This experiment was conducted to determine the influences of supplementing different levels of an additive containing lutein in the diet of Chinese Holstein lactating cows on production performance, antioxidative plasma metabolites, and milk quality. This study was performed on 60 multiparous Holstein dairy cows in peak lactation. The cows were randomly allocated to 1 of 4 homogeneous treatments, with lutein preparation (extracted from marigolds; effective lutein content was 2%) added at levels of 0, 100, 150, and 200g/d per head, with the actual available amounts being 0, 2, 3, and 4g of lutein/d per head, respectively. The experiment lasted for 13wk, with the first week for adaptation. Milk yield and milk compositions were recorded weekly, and milk concentrations of lutein, dry matter intake, and antioxidative blood index were analyzed in the first, fourth, seventh, and thirteenth week of the study. The results showed that adding lutein in the diet had no effect on dry matter intake compared with the control group; however, it slowed down the trend of decline in milk yield, and had a linear incremental effect on milk yield with increasing concentration of lutein. Dietary lutein tended to quadratically increase the percentage of milk fat, and linearly increased milk lactose concentration, with the highest value when treated at 200g of lutein preparation/d per head, and decreased somatic cell count, with the lowest values when treated with 150 and 200g of lutein preparation/d per head. The concentration of lutein in milk linearly increased with the incorporation of the additive, with a value of 0.59, 0.70, 1.20, and 1.50μg/100mL when treated with 0, 100, 150, and 200g/d, respectively. Total plasma antioxidant capacity tended to linearly increase in cows fed lutein preparation, whereas plasma superoxide dismutase and glutathione peroxidase activities did not differ significantly. In conclusion, addition of lutein in the diet could improve the production performance and health status of dairy cows.

Expression Profiling of Glucose Transporter 1 (GLUT1) and Apoptotic Genes (BAX and BCL2) in Milk Enriched Mammary Epithelial Cells (MEC) in Riverine Buffalo during Lactation

Lactation is an important physiological process in dairy animals. During lactation, up to 85% of the body glucose is directed toward the mammary glands for milk synthesis. Studies related to lactation physiology are generally carried out on mammary biopsies, which may adversely affect animal health. In the present study, milk enriched MEC were used to study the expression pattern of GLUT1 and apoptotic genes (BAX and BCL2) across different stages of lactation in riverine buffalo in relation to milk yield. MEC were enriched from milk using cytokeratin-8 antibodies coated magnetic beads. Total RNA isolated from enriched MEC showed significant correlation (r 2 = 0.92 ± 0.02) with the milk yield at different stages of lactation. GLUT1 expression pattern correlated with the milk yield as highest GLUT1 expression (4.68 ± 0.79) was observed during peak-lactation (90 days post-parturition), whereas low GLUT1 expression (1.01 ± 0.1, 15 d; 0.71 ± 0.03, 30 d) was observed during early lactation. The BAX/BCL2 ratio was high (1.02 ± 0.2, 15 d; 0.94 ± 0.06, 30 d) during the early phase of lactation, indicating high rate of apoptosis, whereas low BAX/BCL2 ratio (0.25 ± 0.03, 60 d; 0.42 ± 0.04, 90 d) was observed during mid-lactation coinciding with the increase in RNA concentration and milk yield. Highest BAX/BCL2 ratio (1.41 ± 0.3, 120 d; 4.02 ± 0.6, 240 d) was observed during late lactation i.e., 240 days, which was also reflected as decline in milk yield and RNA concentration. Also, BAX/BCL2 ratio in milk enriched MEC was in accordance with RNA concentration in MEC and milk yield at different phases of lactation. Our study showed that expression pattern of genes under study (GLUT1, BAX, and BCL2) in milk enriched MEC correlated well with important physiological properties such as milk yield in buffalo.

Leistungsminderung und hohe Zellzahlen in einer Milchviehherde nach Verfütterung von hohen Mengen an Biertreber

The present case report describes a herd problem on a Holstein Friesian dairy farm in Switzerland, which could be attributed to the feeding of high amounts of wet brewers' grain over several months. Apathy and reduced general appearance, reduced feed intake as well as a decline in milk yield could be observed. A strong increase in milk somatic cell counts as well as an increase in the incidence of mastitis could be found. The milk fat content was highly elevated in all cows, whereas the milk protein content was reduced. The exclusion of wet brewers' grain from the partial mixed ration resulted in a considerable improvement of the general appearance of the cows and a decrease of the milk somatic cell counts. Feed that is easily spoiled could be a health risk for animals, particularly under hot and humid weather conditions and if fed in high amounts.

Effect of Chronic Hemoplasma Infection on Cattle Productivity

ABSTRACTThe present study evaluated the effect of hemoplasmosis on cattle productivity. Prevalence of bovine hemoplasma was examined by polymerase chain reaction (PCR) using whole blood samples collected from 93 breeding cows and their 71 calves in Hokkaido, Japan. Monthly milk production records and other clinical data were compared between Mycoplasma wenyonii (Mw)-infected, “Candidatus Mycoplasma haemobos” (CMh)-infected, co-infected and PCR-negative groups. Blood chemical parameters were obtained from the 93 cows and 64 calves. PCR results showed that 89.2% (83/93) of cows and 14.1% (10/71) of calves were positive for bovine hemoplasma. Based on productivity data obtained from the 93 cows, Mw-infected, CMh-infected and co-infected cows had significantly lower monthly milk yield compared to PCR-negative cows. Furthermore, decline in milk yield was prolonged in CMh-infected and co-infected groups. No significant differences were found for other clinical findings among the four groups. Calf birth weight tended to be lower for Mw-infected, CMh-infected and co-infected groups compared to the PCR-negative group. There were no significant differences in all blood parameters of cows and calves among the four groups. In addition, no significant differences were found in any parameter between hemoplasma-infected and PCR-negative calves.

Floral Markers of Cornflower (Centaurea cyanus) Honey and Its Peroxide Antibacterial Activity for an Alternative Treatment of Digital Dermatitis

Cornflower (Centaurea cyanus) honey can be characterized by a greenish yellow color and an intense flavor with a bitter aftertaste. Because cornflower honey contains only a limited amount of pollen for the verification of its floral origin, one objective was the characterization of its polyphenol and norisoprenoid contents to assign floral markers. Here, lumichrome (18.8-43.5 mg/kg), 7-carboxylumichrome, (Z/E)-3-oxo-retro-α-ionol, and 3-oxo-α-ionol appeared to be quite suitable for distinguishing cornflower honey from other unifloral honeys. Additionally, due to its comparably high hydrogen peroxide content (0.5-0.9 mM/h) and the associated antibacterial activity, cornflower honey was used as an alternative treatment of digital dermatitis on an organic dairy farm. Cows affected by this hoof disease often show severe lameness and a subsequent decline in milk yield and loss of body condition. The cows' hooves treated with cornflower honey showed significantly faster healing than the control group without any treatment.

Defining and evaluating heat stress thresholds in different dairy cow production systems

Abstract. The aim of this study was to assess the impact of heat stress in dairy cows on test-day records for production traits and somatic cell score (SCS) in the state of Lower Saxony, Germany. Three different production systems were defined: A production system characterized by intensive crop production (=indoor housing), a pasture based production system, and a maritime region. Heat stress was assessed by two temperature-humidity indices (THI) modelled as random regression coefficients in an analysis of variance: One (THIBo) was defined as an average of hourly THI, calculated from hourly recorded temperatures and humidities, the other (THIRa) was based on daily maximal temperature and daily minimal humidity. In all production systems, THIBo=60 and THIRa=70 were identified as general thresholds denoting a substantial decline in test-day milk yield. For daily fat and protein percentage, no universally valid thresholds were identified. In contrast for SCS, especially in the maritime region, heat stress as well as cold stress thresholds were found. Regression analysis was used to study the change in test day milk yield in response to THI of those THI ranges with an obvious decline in milk yield. Regression coefficients were −0.08 kg/THIBo and −0.16 kg/THIRa for the crop production system, −0.17 kg/THIBo and −0.23 kg/THIRa for the pasture based system, and −0.26 kg/THIBo and −0.47kg/THIRa for the maritime region. Based on statistical information criteria, identified thresholds for THIBo should be given preference over THIRa when applying genetic studies on heat stress in German Holstein cows.

Ovariectomy improves lactation persistency in dairy cows

A current trend in the dairy industry is to reduce milk yield at the peak of lactation and improve lactation persistency. Lactation persistency is influenced by livestock management factors, such as feeding level or milking frequency, or by physiological status, including reproductive status or calving period. These factors modulate mammary gland apoptosis and tissue remodeling, which determine the rate of decline of milk yield after the lactation peak. Previous studies on lactating cows suggested that ovarian steroids have a negative effect on milk yield after the peak of lactation. In the present study, 4 Holstein × Normande crossbred multiparous cows were ovariectomized at the time of the lactation peak, and 5 cows underwent sham operations. All of the cows were maintained in lactation for 14mo and milk yield was recorded daily. At slaughter, mammary epithelial cell apoptosis and mammary tissue remodeling were assessed. Ovariectomized cows had improved lactation persistency and presented an average daily milk gain of 2.5kg compared with the sham-operated cows between mo 6 and 14 of lactation. The ovariectomy appears to have limited the decline in the milk yield after the peak of lactation by reducing mammary epithelial cell apoptosis [by reducing poly(adenosine diphosphate-ribose) polymerase expression] and mammary-tissue remodeling (by reducing matrix metalloproteinase activity). In conclusion, removal of ovarian secretion via ovariectomy improved the cows’ lactation persistency.

Relationships between milking frequency, lactation persistency and milk yield in Swedish Red heifers and cows milked in a voluntary attendance automatic milking system

A large dataset comprising output from an automatic milking (AM) system between 1999 and 2006 was examined and a total of 172 cow lactation curves and 68 heifer lactation curves were identified for further analysis. Relationships between milking frequency at different stages of lactation and lactation persistency and total lactation yield were determined. Cows had higher peak and total milk yields than heifers, but heifers had higher persistency (defined as the rate of decline in milk yield between days 100 and 300 post calving). Milking frequency did not differ significantly between cows and heifers in early lactation, but thereafter decreased significantly more in cows than in heifers. The effect of milking frequency on yield characteristics was analysed by comparing the highest and lowest quartiles for milking frequency. High milking frequency in early lactation was consistently associated with increased peak yield. High milking frequency averaged across the whole lactation was associated with increased peak yield in both cows and heifers, and with improved lactation persistency in cows only. This resulted in total lactation yield that was 21% greater in the high quartile cows compared with the low.

Performance and metabolic profile of dairy cows during a lactational and deliberately induced negative energy balance with subsequent realimentation

Homeorhetic and homeostatic controls in dairy cows are essential for adapting to alterations in physiological and environmental conditions. To study the different mechanisms during adaptation processes, effects of a deliberately induced negative energy balance (NEB) by feed restriction near 100 d in milk (DIM) on performance and metabolic measures were compared with lactation energy deficiency after parturition. Fifty multiparous cows were studied in 3 periods (1=early lactation up to 12 wk postpartum; 2=feed restriction for 3 wk beginning at 98±7 DIM with a feed-restricted and control group; and 3=a subsequent realimentation period for the feed-restricted group for 8 wk). In period 1, despite NEB in early lactation [−42 MJ of net energy for lactation (NEL)/d, wk 1 to 3] up to wk 9, milk yield increased from 27.5±0.7kg to a maximum of 39.5±0.8kg (wk 6). For period 2, the NEB was induced by individual limitation of feed quantity and reduction of dietary energy density. Feed-restricted cows experienced a greater NEB (−63 MJ of NEL/d) than did cows in early lactation. Feed-restricted cows in period 2 showed only a small decline in milk yield of −3.1±1.1kg and milk protein content of −0.2±0.1% compared with control cows (30.5±1.1kg and 3.8±0.1%, respectively). In feed-restricted cows (period 2), plasma glucose was lower (−0.2±0.0 mmol/L) and nonesterified fatty acids higher (+0.1±0.1 mmol/L) compared with control cows. Compared with the NEB in period 1, the decreases in body weight due to the deliberately induced NEB (period 2) were greater (56±4 vs. 23±3kg), but decreases in body condition score (0.16±0.03 vs. 0.34±0.04) and muscle diameter (2.0±0.4 vs. 3.5±0.4mm) were lesser. The changes in metabolic measures in period 2 were marginal compared with the adjustments directly after parturition in period 1. Despite the greater induced energy deficiency at 100 DIM than the early lactation NEB, the metabolic load experienced by the dairy cows was not as high as that observed in early lactation. The different effects of energy deficiency at the 2 stages in lactation show that metabolic problems in early lactating dairy cows are not due only to the NEB, but mainly to the specific metabolic regulation during this period.

Nutritional regulation of mammary cell apoptosis in lactating ewes

Recent advances in understanding the control of the mammary cell population now offer new insights to understand the decline in milk yield of dairy animals, which has long been a biological conundrum for the mammary biologists. Evidence indicates that change in mammary cell number is the result of an imbalance between cell proliferation and cell removal and that this is a principal cause of declining production (Stefanon et al., 2001). Further, it suggests that the persistency of lactation, the rate of decline in milk yield with stage of lactation, is strongly influenced by the rate of cell death by apoptosis in the lactating gland (Wilde et al., 1997). The most significant advance in understanding the cell biology underpinning persistency of lactation has come from the demonstration that cell loss during lactation occurs by apoptosis. Several researches obtained in cell cultures in mouse and rat have indicated that gene expression and cellular activities are modulated by the reactive oxygen species

Milk composition and yield changes with advancing pregnancy in dairy buffaloes (Bubalus bubalis)

The changes in the composition of milk with advancing pregnancy were investigated in Nili-Ravi dairy buffaloes. Forty lactating buffaloes were used, within 2-3 months postpartum. The animals were grouped as high, moderate, and low yielders; synchronized for estrus; and inseminated artificially. Milk yield was recorded daily and sampled fortnightly for analysis. The data were analyzed using the univariate weighted mean and general linear model. Decline in milk yield became significant after the 8th week post-conception. The high yielders had the lowest fat contents. Milk fat increased significantly during succeeding weeks post-conception. The highest fat level (8.5%) was observed in week 22. The solid-not-fat (SNF) was higher during the initial 8 weeks. Protein concentration declined with advancing pregnancy. The mineral contents were lower up to 8 weeks and increased later. It was concluded that milk fat concentrations increased linearly from week 2 to 22, while protein showed the opposite pattern in dairy buffaloes. SNF and lactose initially decreased up to week 14 but increased later on. This study suggests that milk composition from dairy buffaloes changes with advancing pregnancy, making it suitable for various types of human consumers.

Short communication: Genetic trends of milk yield under heat stress for US Holsteins

Data included 90,242,799 test-day milk records from 5,402,484 Holstein cows in the first 3 parities and 9,326,754 animals in the pedigree. Additionally, daily temperature-humidity indexes from 202 weather stations were available. Analyses were done by a random regression model in which each parity was treated as a separate trait and that accounted for heat stress. The fixed effects included herd test-day, age at calving, milking frequency, and days in milk classes. Random effects included additive genetic, permanent environment, and herd-year effects, all fit as random regressions. Five covariates in the random regressions included linear splines with 4 knots at 5, 50, 200, and 305 DIM and a function of a temperature-humidity index (THI). Mixed model equations were solved by using an iteration on data approach with a preconditioned conjugate gradient algorithm. Genetic trends for daily milk yield in absence of heat stress (intercept) were 0.140 kg/yr, 0.172 kg/yr, and 0.168 kg/yr for the first, second, and third parity, respectively. Genetic trends for decline of milk yield at temperature of 5°C THI over the threshold of sensitivity to heat stress were −0.002 kg/yr, −0.035 kg/yr, and −0.038 kg/yr, for first, second, and third parity, respectively. Genetic profiles were created by contrasting the 100 most and 100 least heat-tolerant bulls for the official proofs. The most heat-tolerant bulls transmitted lower production and dairy form but higher fertility, productive life, and type, especially udder and locomotion traits. In later parities, the type advantages were smaller. Test-day records capture only a fraction of information due to heat stress, and the real trends for heat stress may be stronger. Studies on heat stress for production should include records on later parities.

Effects of Cooling and Supplemental Bovine Somatotropin on Milk Production relating to Body Glucose Metabolism and Utilization of Glucose by the Mammary Gland in Crossbred Holstein Cattle

Problem statement: The low milk yield and shorter persistency of lactation of dairy cattle is the major problem for the dairy practices in the tropics. High environmental temperatures and rapid decline of plasma growth hormone level can influence milk production. Regulation of the milk yield of animals is mainly based on the mechanisms governing the quantity of glucose extracted by the mammary gland for lactose biosynthetic pathways. The mechanism(s) underlying the effects of cooling and supplemental bovine somatotropin on milk production relating to body glucose metabolism and intracellular metabolism of glucose in the mammary gland of crossbred Holstein cattle in the tropics have not been investigated to date. Approach: Ten crossbred 87.5% Holstein cows were divided into two groups of five animals each. Animals were housed in Normal Shade barn (NS) as non-cooled cows and cows in the second group were housed in barn which was equipped with a two Misty-Fan cooling system (MF) as cooled cows. Supplementation of recombinant bovine Somatotropin (rbST) (POSILAC, 500 mg per cow) were performed in both groups to study body glucose metabolism and the utilization of glucose in the mammary gland using a continuous infusion of [3-3H] glucose and [U- 14C] glucose as markers in early, mid and late stages of lactation. Results: Milk yield significantly increased in both groups during supplemental rbST with a high level of mammary blood flow. Body glucose turnover rates were not significant different between cooled and non-cooled cows whether supplemental rbST or not. The glucose taken up by the mammary gland of both non-cooled and cooled cows increased flux through the lactose synthesis and the pentose cycle pathway with significant increases in NADPH formation for fatty acid synthesis during rbST supplementation. The utilization of glucose carbon incorporation into milk appeared to increase in milk lactose and milk triacylglycerol but not for milk citrate during supplemental rbST in both non-cooled and cooled cows in early and mid lactation. Conclusion: The present study demonstrated that local changes for biosynthetic capacity within the mammary gland would be a factor in identification of the utilization of substrates in the rate of decline in milk yield. The proportion of glucose was metabolized less for lactose synthesis, but metabolized more via the Embden-Meyerhof pathway and the tricarboxylic acid cycle as lactation advanced to late lactation in both cooled and non-cooled cows whether supplemental rbST or not.

Genetic analysis of milk production and composition in crossbred ewes from different maternal genotypes

Milk production and milk composition were measured in 1056 crossbred ewes managed under pasture grazing in a lamb production system. Most ewes were milked on three occasions at ~3, 4 and 12 weeks of lactation. The ewes were the progeny of mainly Merino dams and 91 sires from several maternal crossing breeds including Border Leicester, East Friesian, Finnsheep and Coopworth. The ewes were born over 3 years and run at three sites where they were joined naturally to meat rams. Most of the ewes were first parity (autumn-joined at 7 months of age and spring-joined at 14–17 months of age), with the remainder second or third parity. The cohorts of ewes and sites were linked genetically by three common maternal sires. The 4-h oxytocin-induced milking procedure was used to estimate daily milk production and milk samples were analysed for composition (fat%, protein% and lactose%). Daily milk yield and milk composition traits were analysed using restricted maximum likelihood mixed models procedures. The sire breed of crossbred ewes was significant for milk yield (P < 0.01), fat% (P < 0.01) and lactose% (P < 0.05). There was a significant (P < 0.01) interaction of sire breed × days of lactation, mainly due to the relatively higher milk yield of the East Friesian and White Suffolk cross ewes compared with the other crosses, at the end of the lactation. The East Friesian cross ewes had lower milk fat% than the other cross ewes. Ewes suckling multiple lambs had 29% higher peak milk yield than those bearing and suckling single lambs (P < 0.001). There was an increase in peak milk yield of the ewes from first to second parity, and third parity ewes had a greater decline to the end of lactation causing a significant interaction (P < 0.001). The overall decline in milk yield from peak to late lactation was –21.2 ± 0.7 g/day. Separate analysis showed a significant increase in milk yield with ewe pre-joining weight (regression 6.1 ± 1.8 g/day.kg). The estimate of heritability for daily milk yield was 0.24 ± 0.04 at 90 days of lactation and 0.10 ± 0.02 at 21 days of lactation. The estimates of heritability for the milk composition traits were generally moderate. Estimates of genetic correlations between measurements early and late in the lactation for milk yield and most composition traits were high. The within ewe by stage variance component estimates of repeatability were moderate to high for milk yield, fat% and protein%, with lactose% being low.

Feed supplementation prevents post-conception decline in milk progesterone concentrations associated with production stress in dairy buffaloes (Bubalus bubalis)

The onset of pregnancy may be associated with hormonal changes and decline in milk yield of buffaloes. To investigate this, forty lactating buffaloes from 1st to 23rd weeks post-conception were selected. The animals were assigned to three treatments: PRT, PRS, NPRT and three milk yielding groups HMY, 66 to 75 l/week, n = 12; MMY, 56 to 65 l/week, n = 16; LMY, 46 to 55 l/week, n = 12). Milk samples were collected on alternate weeks and analyzed with ultrasonic milk analyzer. EIA was used for milk progesterone concentrations. Group means were compared and correlation analysis was conducted. Progesterone concentrations increased in almost similar pattern with the advancing weeks post-conception. The high and low yielder showed greater progesterone concentrations in the supplemented than the animals on traditional ration (P < 0.001). Progesterone concentrations correlated positively with fat (%), negatively with milk yield, protein (%) and lactose (%). Decline in milk yield became drastic when progesterone concentrations rose above 6.44 ng/ml. The pregnant animals on traditional ration exhibited a sharper decline in milk yield with the increasing progesterone concentrations as compared to pregnant animals with supplemented ration. It is concluded that concentrates supplementation induced a raise in progesterone levels. Progesterone concentrations and milk yield showed an inverse relationship.

Milk‐production potential of different sward types in a temperate southern Australian environment

SummaryThe milk‐production potential of different sward types was measured in each of the four seasons of the year in a replicated experiment in south‐west Victoria, Australia. Dairy cows were offered ad libitum allowances of a ‘short‐term winter’ sward, based on Italian ryegrass (treatment STW), a ‘long‐term winter’ sward, based on a winter‐active tall fescue (treatment LTW), a ‘long‐term summer’ sward, based on a summer‐active tall fescue (treatment LTS) and a Control sward (perennial ryegrass) in four seasons (days in milk in parentheses): spring (November dairy cows, 124), summer (February, 227), autumn (May, 234) and winter (August, sixty‐four). A ‘short‐term summer’ sward, based on chicory and white clover (treatment STS), was also included in summer. There was a significant season × treatment interaction caused by a more gradual decline in milk yield from peak for cows grazing treatment LTS compared to the Control treatment in the transition period from spring to summer. In summer, cows grazing treatment STS produced more milk (1·41 kg fat plus protein per cow d−1) than cows grazing all other treatments (0·92 kg per cow d−1) because of the superior nutritive value of herbage of pre‐grazing pasture and higher apparent dry‐matter intakes. Swards based on alternative species to perennial ryegrass are capable of supporting milk production that is at least comparable over an annual cycle.