Lactation Persistency Research Articles

Genetic relationship between lactation persistency and conformation traits in Polish Holstein-Friesian cow population

The objective of this study was to find genetic relationships between lactation persistency and conformation traits of Polish Holstein-Friesian cows. The data were derived from SYMLEK - the Polish National Database. The analysis used 22 conformation traits and 3 persistency measures of 18 216 first lactation cows. Persistency was defined as milk yield in the second 100 days in milk (DIM) divided by the yield in the first 100 DIM, milk yield in the third 100 DIM divided by the yield in the first 100 DIM, and milk yield at 280 DIM divided by milk yield at 60 DIM. The lactation curve was modelled with fourth-order Legendre polynomials using a multiple-trait prediction method. The multiple-trait REML method was applied for (co)variance component estimation. The linear model for persistency included fixed effects of herd-year-season of calving, age of calving class, and random animal effect; the linear model for type traits included fixed effects of herd-year-season of calving-classifier, age of calving class, lactation stage, and random animal effect. Stature and composite type traits (except type and conformation) were moderately or strongly genetically correlated with each of the three persistency measures. Genetic correlations of lactation persistency with overall feet and leg score and overall udder score were height and positive, whereas the correlations with stature and size were height but negative. All linearly scored traits had little genetic relationship with persistency measures except for rear udder height, udder width, and foot angle. In these three cases the genetic correlations with persistency measures were relatively high, positive, and preferable. The obtained genetic correlations suggest that increased weights of composite traits like size, overall feet and leg score, and overall udder score in the selection index, as well as selection for better rear udder height and foot angle, might cause a favourable correlated response in persistency.

Effects of season and age at first calving on genetic and phenotypic characteristics of lactation curve parameters in Holstein cows.

In this research data representing 72,946 primiparous cows from 724 herds with 638,063 total test day records calved between 2001 and 2011. These data were analysed to determine the effect of age at first and season of calving on parameters of the Wood lactation curve. Also, genetic trend of the lactation curve parameters in different calving years were evaluated. The results indicate that the highest rate of atypical lactation curve was related to cows that calved in summer (28.05 %). The maximum phenotypic relationship between initial milk yield and total 305-d milk yield was observed in cows calved in spring (0.40). The role of peak yield is more than peak time on 305-d total milk yield in primiparous Holstein. One month increase in age at first calving from 18 to 26 month raised 305-d milk yield by around 138 kg and from 27 to 32 month decreased by 61 kg. The persistency of lactation between 101 and 200 days is higher than that of 201–305 days. Our results indicate that the shape of lactation curve is largely dependent on the season of calving (higher level of milk production in cows which calved in autumn and winter). The heritabilities of parameters of lactation curve and persistency measures were low. The genetic trends for peak time, peak yield and 305-d milk yields were positive and estimated to be 0.019, 0.021 and 8.13 kg/year respectively. So the range from 24 to 26.5 month of calving is the optimum calving time in primiparous Holstein for maximizing 305-d milk yield.

Effects of an individual weight-adjusted feeding strategy in early lactation on milk production of Holstein cows during extended lactation

Extending lactation by voluntarily delaying rebreeding aims to improve fertility and milk production in the modern dairy cow. Previous studies have shown that increased energy concentrations in the ration induced greater total milk yield and lactation persistency defined by the duration and the shape of the lactation curve. In this paper, we hypothesized that increasing the supply of energy during the early lactation mobilization period would have a positive carryover effect on milk production during extended lactation. A total of 53 Holstein cows completed a 16-mo lactation, including 30% primiparous cows. The cows were divided into 2 feeding strategies: half of the cows received a high-energy density diet (HD) in early lactation followed by a lower-energy density diet (LD; strategy HD-LD). The change in diet was defined individually after 42d of lactation, and when the live weight (LW) gain of the cow was ≥0 based on a 5-d average. The other half of the cows were fed the LD diet during the entire lactation (strategy LD-LD). Both groups received 3kg of concentrates per day during milking. Weekly milk composition (fat, protein, lactose, and somatic cells), daily milk production, daily feed intake, daily LW, and body condition score every second week were recorded. The fda package of R was used to model the curves of these different variables for the 53 cows that had a lactation over 400d. The fitted values of these curves and the associated slopes were then compared for parity and treatment effects using a linear mixed-effects model. The HD-LD and LD-LD cows had a similar length of lactation (461±7 d). The HD diet reduced the intensity of the mobilization period and increased the milk production of the multiparous cows in early lactation compared with the cows fed the LD diet. The primiparous cows used the extra energy to grow and gain weight, but not to produce more milk. After the shift in diet, the treatment had little short-term carryover effect on milk yield or LW, but it affected the slopes of some curves. From 0 to 50d from shift, milk fat content of the LD-LD cows decreased faster than that of the HD-LD cows whereas milk lactose increased. From 250 to 350d from shift, the energy-corrected milk decreased faster for the HD-LD cows than for the LD-LD cows. The lactose content in milk decreased faster for the LD-LD cows than for the HD-LD cows, and the fat content in milk was significantly higher for the primiparous HD-LD than for the primiparous LD-LD cows. In conclusion, the supply of extra energy during the mobilization period had a 300-d negative carryover effect on lactation persistency.

Milk production of Holstein-Friesian, Jersey and crossbred cows milked once-a-day or twice-a-day in New Zealand

ABSTRACTThe objective of this study was to compare Holstein-Friesian (F), Jersey (J) and crossbred (F × J) cows milked once-a-day (OAD) or twice-a-day (TAD) in New Zealand for milk, fat and protein yield, lactation persistency and average somatic cell score (SCS). Data consisted of 223,149 herd-test records (89,297 and 133,852 OAD and TAD, respectively) from 11,848 F; 11,677 J and 27,720 F × J spring-calving cows between 2008 and 2012. Compared to TAD systems, cows milked OAD yielded 722, 28.0 and 22.2 kg less milk, fat and protein, respectively. Crossbred and J cows were less affected than F cows by OAD milking with a reduction in milk yield traits of ≤ 19.0%, while in F cows the reduction ranged between 19%–25%. Cows milked OAD had higher SCS than cows milked TAD (6.20 vs. 6.08). The greatest SCS difference in OAD and TAD systems was in first-lactation cows (6.40 vs. 6.02). Persistency of production traits was greater in F and F × J cows milked OAD than in F and F × J cows milked TAD, but J cows had similar milk and protein persistency in both systems. Overall, cows milked OAD had greater persistency than cows milked TAD (79%–90% vs. 76%–85%). These results show that, in commercial herds, the relative difference in production traits between OAD and TAD systems was smaller than those reported in experimental trials.

Some Productive Performance of Egyptian Dairy Buffaloes In Relation to The Reproductive Status

The objective of this present study was to detect the effect of the reproductive status of female dairy buffaloes on some milk production parameters. The study was carried out from the period of ist January 2014 till the end of January 2015. A total number of 252 female dairy buffaloes (aged 3year and 10 months – 7.5 years) of different parities were kept free (loose housing) in partially sheltered yard during day and night all over the year at dairy herd of El- Tawfik dairy farm which locate at Salheia city- sharkeya governorate. The results indicated that day interval milk (DIM) lactation period was 263.12 for buffaloes reared at free range system, Milk yield kg / week (50.13) and lactation to date milk (kg) (1841.90) with mean pregnancy period reached 295.07, appositive correlation coefficient between lactation to date milk to milk yield kg / week and day milk interval at free rang system, high positive correlation coefficient to lactation to date milk and day milk interval , But with negative correlation coefficient by pregnancy period, Day milk interval with positive correlation to lactation to date milk and milk yield kg / week , But with negative correlation coefficient by pregnancy period, a positive correlation coefficient between number of birth to lactation to date milk , day milk interval and pregnancy period , while there was a negative correlation coefficient between number of birth to reproductive status . It could conclude that evaluation of reproductive and dairy performance of buffaloes is essential for economic farming selection in buffalo industry, To increase lactation persistency in addition to total production without occurrence reproduction failure.

Regulation of cell number in the mammary gland by controlling the exfoliation process in milk in ruminants

Milk yield is partly influenced by the number of mammary epithelial cells (MEC) in the mammary gland. It is well known that variations in MEC number are due to cell proliferation and apoptosis. The exfoliation of MEC from the mammary epithelium into milk is another process that might influence MEC number in the mammary tissue. The rate of MEC exfoliation can be assessed by measuring the milk MEC content through light microscopy, flow cytometry analysis, or an immuno-magnetic method for MEC purification. Various experimental models have been used to affect milk yield and study the rate of MEC exfoliation. Reducing milking frequency from twice to once daily did not seem to have any effect on MEC loss in goat and cow milk after 7 d, but increased MEC loss per day in goats when applied for a longer period. An increase in MEC exfoliation was also observed during short days as compared with long days, or in response to an endotoxin-induced mastitis in cows. Other animal models were designed to investigate the endocrine control of the exfoliation process and its link with milk production. Suppression of ovarian steroids by ovariectomy resulted in a greater persistency of lactation and a decrease in MEC exfoliation. Administering prolactin inhibitors during lactation or at dry-off enhanced MEC exfoliation, whereas exogenous prolactin during lactation tended to prevent the negative effect of prolactin inhibitors. These findings suggest that prolactin could regulate MEC exfoliation. In most of these studies, variations of MEC exfoliation were associated with variations in milk yield and changes in mammary epithelium integrity. Exfoliation of MEC could thus influence milk yield by regulating MEC number in mammary tissue.

Associations between milk production level, calving interval length, lactation curve parameters and economic results in Holstein cows

The objective of work was to evaluate effects of milk production level (MY1≥9500 kg, n=23; MY2 = 8000-9499, n=28; and MY3≤7999 kg, n=29) and calving interval length (CI1≥440 days, n=22; CI2 = 400-439 days, n=33; and CI3≤399 days, n=25) on the lactation curve parameters calculated using MilkBot® Model and economic profitability of Holstein dairy cow breeding. Data were obtained from 80 Holstein cows on 1st to 4th parity calved between January and August 2012 on the dairy farm of the Czech University of Life Sciences Prague in Czech Republic. Lactation curve parameters differed more in relation with milk production level compared to calving interval length. Lactation curve in cows with the highest MY was characterized with significantly higher overall magnitude (scale parameter) of milk production (P<0.01), higher peak yield (P<0.01) which occurred later (P<0.05) and higher persistence (P<0.05). Due to combination of higher persistence and total yield, average milk yield per day of calving interval was significantly (P<0.05) higher in cows with middle CI than in short CI. Optimal calving interval length should be assessed in relation with lactation persistence and milk production level. The highest individual profitability was reached by cows in MY1 and CI2 group.

Genotype-by-environment interaction on genetic relationships between lactation persistency and conception measures in Japanese Holstein cows

The objective of this study was to examine the genetic relationships between first-lactation persistency and four measures of conception accounting for heterogeneous genetic (co)variances over a wide range of milk production and fertility management environments. The combination of genotype and management environment conditions (genotype-by-environment (GE) interaction) was studied by using a reaction norm model. Data were obtained on 421,999 cows from 9296 herds for first parity and 257,815 cows from 8318 herds for second parity. Conception status during the first two parities from calving to 70 days in milk (DIM) and 180 DIM were evaluated, leading to a total of four conception measures. Under poor reproductive management, the genetic correlations between first parity lactation persistency and conception to 70DIM were 0.408 and 0.242 for the first and second parities, respectively, compared with 0.178 and 0.116 for the respective genetic correlations between lactation persistency and conception to 180DIM. These positive correlations indicate that increased persistency would help to improve conception to 70DIM or 180DIM. The genetic correlation between persistency and conception to 180 DIM during the first parity was −0.211 under a high level of reproductive management and moderately high milk production, suggesting that conception to 180DIM for low-persistency cows of first parity was increased by improving reproductive management under this situation. In contrast, the genetic correlation between persistency and conception to 180DIM in second parity was 0.351 under high management of milk production and reproduction. The genetic correlations between lactation persistency and conception to 70DIM or 180DIM for the first two parities ranged from negative to positive, depending on the combination of genotype and management environment conditions. Therefore, it is important to consider GE interaction when combining lactation persistency, conception measures, and milk yield to select for sustainable milk production systems.

Milk yield, feed efficiency and metabolic profiles in Jersey and Holstein cows assigned to different fat supplementation strategies

The study aimed to analyse the combined effect of lactation stage and fat supplementation. Either protected or unprotected fat was fed to dairy cows to quantify effects on dry matter intake (DMI), mammary nutrient uptake, energy corrected milk (ECM) yield, milk composition, and energy, N and feed efficiency. Additionally, we studied the effect of adding Hydroxy-methionine-analogue-isobutyrate (HMBi) to the ration supplemented with protected fat. A total of 107 Holstein cows and 54 Jersey cows were assigned to one of four different mixed dietary treatments: Control (CON), control supplemented with whole cracked rapeseed (WCR), control supplemented with rumen protected vegetable fat (Lipmix 40/60, Lipitec, NLM Vantinge Aps, Ringe, Denmark) (RPF), and RPF supplemented with HMBi (MetaSmart, Adisseo, France) (RPFA). Rations contained 2.63%, 5.63%, 5.55%, and 5.59% crude fat on dry matter (DM) basis and 1.77%, 4.29%, 4.59%, and 4.63% FA of DM for CON, WCR, RPF and RPFA, respectively. All cows were offered the same concentrate in the automatic milking system in addition to the mixed rations. After calving, cows were fed CON until they had gained 11kg (Jersey) or 15kg (Holstein) body weight, compared to their lowest recorded weight after calving. Subsequently, the cows were randomly assigned to one of the four treatments until the end of lactation. There was no effect of feeding strategy on DM intake during week 9–40 of lactation. Fat supplemented rations (WCR; RPF) increased yield of milk, ECM and lactose, but decreased milk protein and urea concentrations compared to CON. No effects of HMBi on milk yield and composition were detected. Lactation persistency was improved for all fat supplemented treatments for multiparous cows, particularly with WCR. Fat supplemented rations decreased energy efficiency in Jersey cows but increased energy efficiency in Holstein cows. Because fat supplementation reduced dietary protein concentration and increased milk production, protein intake was lower and N efficiency was higher on WCR and RPF than on CON. Metabolite concentrations in jugular vein blood plasma and concentration differences between jugular and milk veins, which reflect nutrient uptake by the mammary gland, were not affected by the ration fed, breed, or time from calving until ration change. In conclusion, fat supplementation during weeks 9–40 of lactation increased ECM yield and N efficiency irrespective of source of fat, whereas additional supplementation of HMBi showed no effect. The effect of fat persisted throughout lactation.

Experiencia clínica con un anticonceptivo hormonal inyectable de depósito

207 mujeres peruanas altamente fértiles fueron estudiados con un anticonceptivo hormonal de larga duración; este compuesto era un gestágeno sintético: enantato de noretindrona; con una dosis de 200 mg. cada tres meses, no hubo embarazos en un grupo de 134 pacientes. En 53 pacientes que recibieron la dosis algunos cada 4 meses se produjeron 3 embarazos, lo que demuestra la reversibilidad del mecanismo anticonceptivo. No se observaron efectos secundarios en los primeros 3 meses con la incidencia habitual de anticonceptivos orales, pero disminuyó a 2,9% después de este período de tiempo. Los autores comentan la persistencia de la lactancia y la desaparición de la dismenorrea que se produjo en la mayoría de los pacientes.

Milk yield differences between 1× and 4× milking are associated with changes in mammary mitochondrial number and milk protein gene expression, but not mammary cell apoptosis or SOCS gene expression

Milking frequency is known to affect milk production and lactation persistence in dairy cows. Despite this, the mechanisms underlying this effect are only partially understood. Previous work in dairy cows examining increases in milk yield due to increased milking frequency have identified changes in apoptosis and expression of genes regulating cytokine signaling. In addition, changes in mitochondrial biogenesis and function have been suggested to play a role during the lactation cycle in regulating milk production. The goal of this study was to test the hypothesis that, when maintained over an entire lactation, extreme differences in milking frequency would be reflected in differences in apoptosis, mammary mitochondrial number, and the mammary expression of genes known to inhibit cytokine signaling. Primiparous Holstein cows (n=6) were assigned to the study 40d before parturition after which 1 udder half was milked once daily (1×) and the other 4 times daily (4×) Mammary biopsies were collected at 15, 60, 120, and 230d of lactation. Average milk yield from the 4× side was 3 times higher than from the 1× side. Analysis of milk composition revealed that protein, lactose, and solids-not-fat percentages were lower in 1× than 4× udder halves. Mammary cell apoptosis was not affected by milking frequency. Mammary cell mitochondrial number, as estimated by succinate dehydrogenase staining, was higher in early lactation, decreasing as days in milk increased, and with increased milking frequency. Although mammary expression of α-lactalbumin (LALBA) and β-casein (CSN2) was significantly increased in 4× glands, the expression of suppressors of cytokine signaling were similar between 1×- and 4×-milked halves. These results support the conclusion that changes in milk production in response to extreme differences in milking frequency may be related to alterations in mitochondrial number and lactose synthesis, but not apoptosis.

Analyzing the heterogeneity of farmers’ preferences for improvements in dairy cow traits using farmer typologies

Giving consideration to farmers’ preferences for improvements in animal traits when designing genetic selection tools such as selection indexes might increase the uptake of these tools. The increase in use of genetic selection tools will, in turn, assist in the realization of genetic gain in breeding programs. However, the determination of farmers’ preferences is not trivial because of its large heterogeneity. The aim of this study was to quantify Australian dairy farmers’ preferences for cow trait improvements to inform and ultimately direct the choice of traits and selection indexes in the 2014 review of the National Breeding Objective. A specific aim was to analyze the heterogeneity of preferences for cow trait improvements by determining whether there are farmer types that can be identified with specific patterns of preferences. We analyzed whether farmer types differed in farming system, socioeconomic profile, and attitudes toward breeding and genetic evaluation tools. An online survey was developed to explore farmers’ preferences for improvement in 13 cow traits. The pairwise comparisons method was used to derive a ranking of the traits for each respondent. A total of 551 farmers fully completed the survey. A principal component analysis followed by a Ward hierarchical cluster analysis was used to group farmers according to their preferences. Three types of farmers were determined: (1) production-focused farmers, who gave the highest preference of all for improvements in protein yield, lactation persistency, feed efficiency, cow live weight, and milking speed; (2) functionality-focused farmers with the highest preferences of all for improvements in mastitis, lameness, and calving difficulty; and (3) type-focused farmers with the highest preferences of all for mammary system and type. Farmer types differed in their age, their attitudes toward genetic selection, and in the selection criteria they use. Surprisingly, farmer types did not differ for herd size, calving, feeding system, or breed. These results support the idea that preferences for cow trait improvements are intrinsic to farmers and not to production systems or breeds. As a result of this study, and some bioeconomic modeling (not included in this study), the Australian dairy industry has implemented a main index and 2 alternative indexes targeting the different farmer types described here.

Inferring causal relationships between reproductive and metabolic health disorders and production traits in first-lactation US Holsteins using recursive models

Health disorders in dairy cows have a substantial effect on the profitability of a dairy enterprise because of loss in milk sales, culling of unhealthy cows, and replacement costs. Complex relationships exist between health disorders and production traits. Understanding the causal structures among these traits may help us disentangle these complex relationships. The principal objective of this study was to use producer-recorded data to explore phenotypic and genetic relationships among reproductive and metabolic health disorders and production traits in first-lactation US Holsteins. A total of 77,004 first-lactation daughters’ records of 2,183 sires were analyzed using recursive models. Health data contained information on reproductive health disorders [retained placenta (RP); metritis (METR)] and metabolic health disorders [ketosis (KETO); displaced abomasum (DA)]. Production traits included mean milk yield (MY) from early lactation (mean MY from 6 to 60d in milk and from 61 to 120d in milk), peak milk yield (PMY), day in milk of peak milk yield (PeakD), and lactation persistency (LP). Three different sets of traits were analyzed in which recursive effects from each health disorder on culling, recursive effects of one health disorder on another health disorder and on MY, and recursive effects of each health disorder on production traits, including PeakD, PMY, and LP, were assumed. Different recursive Gaussian-threshold and threshold models were implemented in a Bayesian framework. Estimates of the structural coefficients obtained between health disorders and culling were positive; on the liability scale, the structural coefficients ranged from 0.929 to 1.590, confirming that the presence of a health disorder increased culling. Positive recursive effects of RP to METR (0.117) and of KETO to DA (0.122) were estimated, whereas recursive effects from health disorders to production traits were negligible in all cases. Heritability estimates of health disorders ranged from 0.023 to 0.114, in accordance with previous studies. Similarly, genetic correlations obtained between health disorders were moderate. The results obtained suggest that reproductive and metabolic health disorder and culling due to metabolic and reproductive diseases have strong causal relationships. Based on these results, we concluded that a health disorder (either reproductive or metabolic) occurring in early lactation has a moderate causal effect on the reproductive or metabolic health disorder occurring in later lactation. In addition, direct, indirect, and overall effects of reproductive and metabolic health disorders on milk yields for cows that avoid culling are weak.

Comparative expression profiling of insulin-like growth factor binding protein-5 in milk of Bos indicus and Bubalus bubalis during lactation

Insulin-like growth factor binding protein-5 (IGFBP-5) is a key molecule in mammary gland development, which facilitates the removal of mammary epithelial cells (MECs) by apoptosis that takes place during remodeling of the mammary gland during involution. IGFBP-5 binds with IGFs for their bioavailability. IGFBP-5 has been reported to perform pleiotropic roles such as cellular apoptosis, proliferation and differentiation. To understand the role of IGFBP-5 during lactation and clinical mastitis, expression profiling of IGFBP-5 at the protein level was performed in both indigenous cows (Bos indicus) and buffaloes (Bubalus bubalis) belonging to two different breeds – Sahiwal cows and Murrah buffaloes. Reverse-transcriptase PCR (RT-PCR) of IGFBP-5 mRNA confirmed its expression in milk somatic cells and MECs of Sahiwal cows. ELISA was performed for quantitative measurement of IGFBP-5 concentrations in milk during different days (0, 50, 100, 150, 200, 250 and 300) of lactation, during the involution period and in animals exhibiting short lactation and clinical mastitis. The highest concentration of IGFBP-5 in milk was observed during the involution period followed by colostrum, late and early lactation, respectively, in both cattle and buffaloes. No significant difference in the concentration of IGFBP-5 was observed during the first 150 days of lactation between cows and buffaloes. However, higher concentration of IGFBP-5 was observed in cows during late lactation (200 to 300 days) in comparison with buffaloes. To validate the ELISA data, quantitative real-time PCR was performed in MECs of Sahiwal cows. The relative mRNA abundance of IGFBP-5 was found to be significantly (P<0.05) higher on day 15 than between 50 and 150 days of lactation in case of Sahiwal cows. Highest mRNA expression of IGFBP-5 was observed around 300 days of lactation followed by 200 and 250 days (P<0.05), respectively. Murrah buffaloes showed low levels of IGFBP-5 protein in milk as compared with Sahiwal cows during lactation in ELISA. Animals having history of short lactation length (short lactating animals) showed higher levels of IGFBP-5 expression (at protein level) in comparison with normal lactating animals. We propose that higher level IGFBP-5 expression may have functional significance in lactation persistency. As a pro-apoptotic molecule, higher expression of IGFBP-5 was observed to be inversely related to lactation length and milk production.

Lactation Curve and Persistency of Anatolian Buffaloes

The aim of this study was to determine the lactation curve traits of Anatolian buffaloes raised under different conditions in farms in Tokat Province, Turkey. Wood’s gamma curve parameters were employed to identify the lactation curve types, and values for the parameters beginning yield (a), coefficient of rising (b) and coefficient of decreasing (c) were used to determine the shape and type of lactation curve. All parameters in typical lactation curves were positive, and in the event of one parameter being negative, the curve was considered to be an atypical lactation curve. A total of 690 lactation curves were investigated. It was determined that 406 (58.84%) of these curves were typical, while 90 (13.04%) were concave and 194 (28.12%) of a decreasing type. For typical lactation curves, a, b, c, persistency (S), time after parturition until the peak yield occurs (Tmax), maximum daily peak yield (Ymax), and coefficient of determination (R2) were 7.14±0.008, 0.85±2.1, 0.40±0.001, 2.68, 63.6, 6.41 and 76.33, respectively. For concave lactation curves, values for a, b, c, Tmax, Ymax and R2 were 4.94±0.42, -0.73±0.016, - 0.23±0.0038, 95.40, 7.41±0.004 and 71.68, respectively. For decreasing typical lactation curves, values for a, b, c, Tmax, and R2 were 5.31±0.0041, -0.15±0.007, 0.039±0.0023, 3.89±0.11 and 79.94, respectively. Parameters predicted by the Wood model within the scope of this study have the potential of being useful for breeding programmes. Further breeding/selection activities could be conducted by using the female Anatolian buffaloes with typical lactation curves.

A review of the genetic and non-genetic factors affecting extended lactation in pasture-based dairy systems

Milk production per cow has significantly increased over the last 50 years due to the strong genetic selection for increased milk production; associated with this increased production has been a decline in reproductive performance. As a result, superior-yielding cows that have failed to get into calf in a traditional 12-month calving system may be carried over and milked continuously for another 6 months instead of being culled. Studies indicate that cows are able to achieve lactations greater than 305 days and up to 670 days under pasture-based systems, with and without the use of supplementary feeds. Extended lactations of 16 months are most common and economically viable in Australian dairy systems. These findings indicate a potential role for extended lactation in countries such as Australia, where pasture-based dairy systems in which Holstein-Friesian dairy cows predominate. However, variation between cows in their milk yield profiles and the ability of cows to reach a planned dry-off date over an extended lactation occurs depending on the cow’s genetic strain, nutrition and environmental interactions, with certain strains of cow being better suited to extended lactation than others. The focus of this review is to examine the scope for genetic improvement as well as important considerations (non-genetic factors) when selecting suitable animals for extended lactation in pasture-based dairy systems, with an emphasis on Australian systems. These considerations include the impacts of cow strain, nutrition, milk production, and biological and economical costs associated with extended lactation. Methods for modelling extended lactation and estimating genetic parameters of lactation persistency, milk yield and component traits under extended lactation will be addressed and future directions for further research suggested.

Genetic correlations among female fertility, 305-day milk yield and persistency during the first three lactations of Japanese Holstein cows

The genetic correlations between reproductive traits in cows and milk-production traits (305-day milk yield and lactation persistency) were estimated by using first-lactation records (representing 476,284 Japanese Holstein cows), second-lactation records (380,474 cows), and third-lactation records (267,344 cows). The reproductive traits evaluated were: days from calving to the first insemination (DCF); conception rate for the first insemination (CR); number of inseminations (NI); and days open (DO). Persistency was defined as the difference between milk yields at 240 and 60 days in milk. Genetic parameters for reproductive traits (DCF, CR, NI, and DO) were estimated within each lactation by using a four-trait animal model. The genetic correlations between reproductive traits and milk-production traits were estimated by using a three-trait (one reproductive trait and two milk production traits) linear model. The genetic correlation estimates within the first lactation were similar to those of the other lactations, suggesting that the genetic relationships among fertility, 305-day milk yield, and lactation persistency were constant over the first three lactations. The genetic correlations among reproductive traits were fairly strong, but those of DCF with CR and NI were relatively weak. Antagonistic genetic correlations, which ranged from 0.17 to 0.39 in absolute value, between reproductive traits and persistency were revealed. Therefore, when selecting to increase lactation persistency, indicators of female fertility have to be included in the genetic evaluation to reduce undesirable side effects on fertility in cows.

Mammary stem cells: expansion and animal productivity.

Identification and characterization of mammary stem cells and progenitor cells from dairy animals is important in the understanding of mammogenesis, tissue turnover, lactation persistency and regenerative therapy. It has been realized by many investigators that altered lactation, long dry periods (non-milking period between two consecutive lactation cycles), abrupt cessation of lactation (common in water buffaloes) and disease conditions like mastitis, greatly reduce milk yield thus render huge financial losses within the dairy sector. Cellular manipulation of specialized cell types within the mammary gland, called mammary stem cells (MaSCs)/progenitor cells, might provide potential solutions to these problems and may improve milk production. In addition, MaSCs/progenitor cells could be used in regenerative therapy against tissue damage caused by mastitis. This review discusses methods of MaSC/progenitor cell manipulation and their mechanisms in bovine and caprine animals. Author believes that intervention of MaSCs/progenitor cells could lessen the huge financial losses to the dairy industry globally.

Technical note: A noninvasive method for measuring mammary apoptosis and epithelial cell activation in dairy animals using microparticles extracted from milk

Milk production from dairy animals has been described in terms of 3 processes: the increase in secretory cell numbers in late pregnancy and early lactation, secretion rate of milk per cell, and the decline in cell numbers as lactation progresses. This latter process is thought to be determined by the level of programmed cell death (apoptosis) found in the animal. Until now, apoptosis has been measured by taking udder biopsies, using magnetic resonance imaging scans, or using animals postmortem. This paper describes an alternative, noninvasive method for estimating apoptosis by measuring microparticles in milk samples. Microparticles are the product of several processes in dairy animals, including apoptosis. Milk samples from 12 Holstein cows, at or past peak lactation, were collected at 5 monthly samplings. The samples (n=57) were used to measure the number of microparticles and calculate microparticle density for 4 metrics: annexin V positive and merocyanine 540 dye positive, for both and total particles, in both whole milk (WM) and spun milk. Various measures of milk production were also recorded for the 12 cows, including daily milk yield, fat and protein percentage in the milk, somatic cell count, and the days in milk when the samples were taken. A high correlation was found between the 4 WM microparticle densities and days in milk (0.46 to 0.64), and a moderate correlation between WM microparticle densities and daily milk yield (−0.33 to −0.44). No significant relationships were found involving spun milk samples, somatic cell count, or fat and protein percentage. General linear model analyses revealed differences between cows for both level of microparticle density and its rate of change in late lactation. Persistency of lactation was also found to be correlated with the WM microparticle traits (−0.65 to −0.32). As apoptosis is likely to be the major contributor to microparticle numbers in late lactation, this work found a noninvasive method for estimating apoptosis that gave promising results. Further investigation is required to find out the factors affecting microparticle production and how it changes throughout lactation.

Milk yield and composition from Angus and Angus-cross beef cows raised in southern Brazil.

This study assessed milk yield and composition of Angus and Angus-cross beef cows raised in southern Brazil. A total of 128 records were collected in 2 consecutive calving seasons from cows between 3 and 5 yr of age of 4 breed compositions: Angus (ANAN), Caracu × Angus (CRAN), Hereford × Angus (HHAN), and Nelore × Angus (NEAN). These cows were mated to Brangus (BN) or Braford (BO) bulls and managed under extensive grazing conditions in southern Brazil. Milk production of these cows was assessed by 2 procedures: indirectly by the calf weigh-suckle-weigh procedure (WD) and directly by machine milking (MM). Lactation curves were estimated using nonlinear regression and the following related traits were derived: peak yield (PY), peak week (PW), total yield at 210 d (TY210), and lactation persistence (PERS). Milk composition and calf weaning weight adjusted to 210 d (WW210) were also determined. The MM technique was considered more accurate because of lower standard errors of estimated means, greater statistical power, and greater correlation between TY210 and WW210 (0.50) compared to WD (0.36). Considering the more precise evaluation by MM, the CRAN and NEAN cows had greater TY210 (1070 and 1116 kg, respectively) and PY (8.1 and 7.8 kg, respectively) compared to ANAN and HHAN cows, which had 858 and 842 kg for TY210 and 6.6 and 6.3 kg for PY, respectively. The NEAN cows had the latest PW at 10.8 wk. Late-calving cows had 21% lower TY210 compared to cows that calved earlier. Milk composition was influenced by cow genotype, with CRAN and NEAN cows producing milk with greater fat (3.8 and 3.9%, respectively) and protein (3.2 and 3.1%, respectively) content compared to ANAN and HHAN cows. Regardless of the genotype, fat, protein, and total solids increased in concentration from beginning to end of lactation, while lactose content decreased. Crossbreeding of Angus with adapted breeds of taurine or indicine origin can be effective in increasing milk yield and nutrient content and, consequently, producing heavier calves at weaning under extensive grazing in southern Brazil and other similar subtropical climate regions.