Effects of secretion removal on bovine mammary gland function following an extended milk stasis.

The objective of this study was to determine whether lactation function could be reinitiated after a period of extended milk stasis. Involution was induced by milk stasis in lactating Holstein cows for a period of 11 d. On d 11, one side of the mammary gland was milked twice daily for 3 d. The contralateral side remained unmilked for the 14-d experimental period. Cows were slaughtered, and mammary tissue was collected from both udder halves for further analysis. Mammary secretion volume was partially restored in the milked udder half, but reestablished milk yields were variable among cows. A partial recovery of lactation function was further indicated by elevated levels of lactose and protein profiles resembling milk in mammary secretions from the milked glands. Lactose and protein profiles from the unmilked glands were similar to those of glands undergoing involution. Lactoferrin levels were elevated in secretions from the milked and unmilked udder halves. Casein and lactoferrin synthesis by mammary explants and beta-casein and lactoferrin mRNA abundance in mammary tissues corresponded to protein profiles from milked and unmilked mammary secretions. alpha-Lactalbumin mRNA was variable but was more abundant in the milked glands compared with the unmilked glands. Lectin fluorescence microscopy for soybean agglutinin preferentially stained the apical surface of the mammary epithelial cells from the milked glands. Staining was absent in the unmilked glands and suggested resumption of lactation function in all such milked glands. These results suggest that mammary involution can be partially reversible after 11 d of milk stasis.     

Growth of Corynebacterium bovis in mammary secretions during physiological transitions of the bovine mammary gland

An in vitro microassay was used to evaluate growth of five strains of Corynebacterium bovis in mammary secretions collected from quarters of five Holstein cows at 0, 14, and 28 d of involution, at parturition, and 14 d after parturition. Variation in growth among different strains of Corynebacterium bovis was observed. Corynebacterium bovis grew well in mammary secretions obtained at the last milking of lactation, at parturition, and 14 d after parturition. However, growth of four strains of Corynebacterium bovis in mammary secretions obtained at 14 and 28 d of involution was reduced significantly. In contrast, a streptomycin-resistant strain of Corynebacterium bovis grew well in mammary secretions obtained during involution. These data suggest that mammary secretions support growth of Corynebacterium bovis during lactation but inhibit growth during the nonlactating period. Inhibition of growth in secretions collected during the nonlactating period may be associated with the high rate of spontaneous elimination of Corynebacterium bovis intramammary infection from cessation of milking to parturition. Conversely, enhanced growth in milk may be related to persistent Corynebacterium bovis intramammary infections during lactation.     

Influence of nonlactating and peripartum bovine mammary secretions on growth of Staphylococcus species

Bovine mammary secretions from individual quarters were collected from five cows at 0, 14, and 28 d of involution, at parturition, and 14 d after parturition and used in a microassay to evaluate growth of several Staphylococcus species. All Staphylococcus species evaluated followed similar growth patterns in secretions. Mammary secretions obtained at 14 and 28 d of involution were poor media for growth of Staphylococcus species. Conversely, mammary secretions collected at cessation of milking, parturition, and early lactation supported growth of all species evaluated. Growth of Staphylococcus species in mammary secretions differed slightly among cows but was similar among quarters of a cow. Results suggested that the ability of bovine mammary secretions to support or inhibit growth of Staphylococcus species was related to functional states of the mammary gland.     

Natural protective factors in bovine mammary secretions following different methods of milk cessation

Bovine mammary secretions were obtained during late lactation and early involution to determine if different methods of milk cessation influenced milk yield, composition, and in vitro growth of coliform mastitis pathogens. Cows (n = 8/group) producing about 13 kg of milk prior to experimentation were dried off by abrupt or intermittent milk cessation. An additional group was dried off by intermittent milk cessation and fed only hay during the last week of lactation. Cows milked intermittently produced significantly less milk during the last week of lactation than cows dried off by abrupt milk cessation. Mammary secretions from cows milked intermittently and fed only hay contained higher concentrations of somatic cells, lactoferrin, immunoglobulin G, and bovine serum albumin, a lower citrate:lactoferrin molar ratio, and were more inhibitory to in vitro growth of Escherichia coli and Klebsiella pneumoniae throughout most of the experimental period than mammary secretions from cows dried off by intermittent or abrupt milk cessation. Few differences in mammary secretion composition or in vitro growth of mastitis pathogens were observed between cows dried off by intermittent or abrupt milk cessation. Data suggest that growth of mastitis pathogens in mammary secretions may be related to natural protective factors, which can be manipulated by different methods of milk cessation.     

Early mammary gland metabolic and immune responses during natural-like and forceful drying-off in high-yielding dairy cows

The present work compared metabolic and immune responses in genetically high-producing cows that produced a low amount of milk before expected involution and in cows with the same genetic potential that produced copious amounts of milk before their scheduled drying-off. Ten multiparous lactating Israeli Holstein cows producing approximately 10,500 L in the current lactation, without bacterial infection and scheduled for drying-off approximately 60 d before their expected parturition, were studied. Five of the cows that exhibited a sharp, spontaneous reduction in milk yield at the end of their lactation and produced less than ~14 L/d were defined as cows approaching natural involution (ANI), and 5 cows that produced between 25 and 35 L/d were defined as cows approaching forced involution (AFI). Three days before scheduled drying-off, milking was stopped and milk samples were collected from each quarter. After milking cessation, only modest swelling was observed in the udders of the ANI cows. In the ANI cows, lactose and fat concentrations decreased and the fat:lactose concentration ratio indicated that on d 1 and 2 fat concentrations decreased faster than lactose concentration, whereas on d 3, the rate of reduction was about the same for lactose and fat. In contrast, in AFI cows, fat concentrations increased on d 1 and the fat:lactose ratio indicated that changes in fat secretion were minor compared with those of lactose secretion. Rennet clotting time of milk after drying-off in the ANI cows increased, whereas curd firmness decreased rapidly, such that mammary secretions did not coagulate on d 3. In the AFI cows, such significant changes were observed only on d 3. The inflammatory response increased in both groups, but at each stage the increase was greater in ANI cows than in AFI cows. On d 1, the increase in leukocyte numbers in the ANI cows was made up of mononuclear cells (i.e., T lymphocytes and macrophages). In contrast, in the AFI cows, we observed a marked increase in leukocyte numbers, mainly in the form of polymorphonuclear cells. Our data indicate that the abrupt mammary involution induced in AFI cows provoked signs of distress, which were associated with neutrophilia in milk. In contrast, in the ANI cows, cessation of milking occurred without evidence of engorgement of the udder. Physiological differences in ANI and AFI cows are distinct and are reflected in the differences in the leukocyte populations in milk.     

Short communication: suppression of estrous cycles in lactating cows has no effect on milk production

The decline in milk yield observed after peak production in dairy animals results from apoptotic death of mammary epithelial cells. In cows, this decrease in milk yield can be accelerated by injection of 17β-estradiol, thus evoking a possible role of estrogens in the regulation of bovine mammary gland involution. In nonpregnant cows, mammary involution could be induced or enhanced by the return of estrous cycles and the accompanying cyclic peaks of estrogen concentration in the serum of lactating animals. To test this hypothesis, we inserted implants of a GnRH agonist, deslorelin, in an ear of each cow (n = 10) on d 10 and 100 of lactation, to temporarily suppress the return of ovarian cycles. Cows were studied from calving to d 210 of lactation. Deslorelin had no impact on feed intake or animal health. Deslorelin significantly reduced serum concentrations of 17β-estradiol and progesterone as compared with untreated cows (n = 10). Deslorelin had no effect on milk fat and protein, whereas milk lactose content was lower in treated cows than in control cows on d 100 of lactation. Finally, there was no difference in milk production between the 2 groups of cows. These results are consistent with previous observations that showed that delaying estrous cycles after calving had no effect on milk yield and they extend those observations to late lactation. Based on milk production data, the estrogen profiles associated with recurring estrous cycles apparently do not cause bovine mammary tissue to undergo gradual involution.     

Short communication: Repeated mammary tissue collections during lactation do not alter subsequent milk yield or composition

Mammary biopsy collection (MB) is a valuable approach for studying mammary gland biology, but it is unclear if repeated MB impair the performance of lactating dairy cows. The objective of this trial was to examine the effect of repeated MB during lactation on udder health, dry matter intake (DMI), and lactation performance of lactating dairy cows. Sixty-four multiparous, mid-lactation Holstein cows were enrolled in a 29-wk trial, and 32 cows were randomly selected for repeated MB. The MB and non-MB (NMB) cows had similar parity (2.6 ± 0.9) and days in milk (96.5 ± 56.3 d) at enrollment. All animals were housed in the same barn and managed in the same manner. Cows were milked 3 times daily with milk yield recorded at each milking. Milk composition was measured weekly and DMI recorded daily. Three MB were performed per cow: 1 wk after enrollment and at 15 and 24 wk. The first and third MB were performed on the left rear quarter, whereas the second MB was on the right rear quarter. The MB were performed based on previously described procedures using a rotating stainless steel cannula with a retractable blade connected to a cordless drill, with appropriate sedation and antiseptic treatment after each MB. After MB, udder health, surgical wound healing, and presence of blood in milk were visually examined at each milking. Blood was cleared from milk 3.86 ± 2.0 d after MB. During the experiment, 4 rear quarters of MB cows and 5 rear quarters from NMB cows were diagnosed and treated for clinical mastitis. No differences were observed in DMI, milk yield, somatic cell score, or milk concentration and yields of fat, protein, lactose, and solids-not-fat between MB and NMB. In conclusion, lactating cows recover rapidly from MB, and repeated MB have no long-term effects on DMI, milk yield and composition, or udder health of lactating dairy cows.     

Inhibiting prolactin by cabergoline accelerates mammary gland remodeling during the early dry period in dairy cows

The inhibition of prolactin release using cabergoline, a dopamine agonist, is an effective strategy to accelerate the changes in mammary secretion composition after drying-off. The objective of this study was to determine how cabergoline may affect mammary tissue remodeling during early involution. Holstein dairy cows were treated with either a single i.m. administration of 5.6 mg of cabergoline (Velactis, Ceva Santé Animale, Libourne, France, n = 7) or placebo (n = 7) at the time of drying-off. Mammary biopsy samples were collected 1 wk before drying-off (d ?6), after 30 h of milk accumulation (d 1), and again 8 d following drying-off (d 8) to determine changes in gene expression, lactoferrin content, and cell turnover. Blood and mammary secretion samples were collected at d ?6 and again at d 1, 2, 3, 4, 8, and 14 following the abrupt cessation of lactation to evaluate indicators of blood-milk barrier integrity and other markers of mammary tissue remodeling. Cabergoline induced less SLC2A1, BAX, CAPN2, and IGFBP5 mRNA expression. In contrast, cabergoline did not modify changes in cell proliferation and apoptosis. Following the cessation of lactation, changes in mammary secretion composition (Na⁺ and K⁺) and blood lactose concentrations were indicative of a loss in the blood-milk barrier function in both treatment groups. Cabergoline treatment affected only Na⁺ and K⁺ concentrations at d 1, suggesting a moderate increase in tight junction permeability. The increase in the activity of MMP9 and in mammary epithelial cell concentration in mammary secretions was greater in cabergoline-treated cows than in control cows, suggesting more mammary tissue remodeling. The increase in lactoferrin immunostaining in the mammary tissue occurred earlier for cabergoline-treated cows than for control cows, and was essentially localized in the stroma. Changes in some key markers of mammary involution suggest that cabergoline accelerates mammary gland remodeling. Thus, a single injection of cabergoline after the last milking would facilitate drying-off by enhancing mammary gland involution.     

Current concepts on the role of oxytocin in milk ejection

Timing of oxytocin release may influence milk ejection. Oxytocin is higher in cows after manual premilking stimulation than in cows receiving no stimulation. Premilking stimulation offers no advantages to milk production in short trials but results in shorter times of machine on and higher average rate of milk flow. Enhanced mechanical stimulation does not seem as effective as manual stimulation in short trials. Oxytocin release is multiphasic, and contents in blood decline during milking. Maximal concentrations during milking decrease across lactation. Nonlactating cows also release oxytocin upon udder stimulation and conditioning. Virgin heifers do not respond in the same way to udder stimulation as lactating cows, thus suggesting that sensitivity of the milk ejection reflex depends upon the physiological state of the animal. Cows probably release about one-third of their stores of oxytocin at milking, and it appears that little hormone is necessary for effect at the udder. Basal concentrations of oxytocin decrease from early to midlactation and increase from mid to late lactation and from late lactation to involution. Half-lives, metabolic clearance rates, and entry rates for oxytocin were measured in cattle in various physiological states. Data from these measurements are discussed.     

Responses of dairy cows with divergent residual feed intake as calves to metabolic challenges during midlactation and the nonlactating period

Residual feed intake (RFI) is defined as the difference between the actual and expected feed intake required to support animal maintenance and growth. Thus, a cow with a low RFI can obtain nutrients for maintenance and growth from a reduced amount of feed compared with a cow with a high RFI. Variation in RFI is underpinned by a combination of factors, including genetics, metabolism, thermoregulation and body composition; hypothalamic-pituitary-adrenal (HPA) axis responsiveness is also a possible contributor. Responses to 3 metabolic challenges were measured in lactating and nonlactating dairy cattle. Sixteen Holstein Friesian cows with phenotypic RFI measurements that were obtained during the growth period (188–220 d old) were grouped as either low-calfhood RFI (n = 8) or high-calfhood RFI (n = 8). An ACTH (2 µg/kg of body weight), insulin (0.12 U/kg), and epinephrine (a low dose of 0.1 µg/kg and a high dose of 1.6 µg/kg of epinephrine) challenge were each conducted during both midlactation (122 ± 23.4 d in milk) and the nonlactating period (dry period; approximately 38 d after cessation of milking). Cows were housed in metabolism stalls for the challenges and were fed a diet of alfalfa cubes ad libitum for at least 10 d before the experiment (lactating cows also were offered a total of 6 kg of dry matter/d of crushed wheat grain plus minerals fed as 3 kg of dry matter at each milking) and were fasted for 12 h before the challenges. The efficiency of conversion of feed into milk (the ratio of feed consumed to milk produced over the 7 d before the experiment) during midlactation was better (lower) in low-calfhood RFI cows, although dry matter intake did not differ between RFI groups. Low-calfhood RFI cows exhibited a lower plasma cortisol response to the ACTH challenge than high-calfhood RFI cows, particularly in midlactation (?15%). The low-calfhood RFI cows had a greater plasma insulin-like growth factor-1 response to the insulin challenge and plasma fatty acid response to epinephrine compared with the high-calfhood RFI cows. These data suggest that high-calfhood RFI cows exhibit a more responsive HPA axis. As divergence in RFI measured during growth is retained (although reduced) during lactation, it is possible that energy is used to respond to HPA axis activation at the expense of production in high-calfhood RFI dairy cattle during lactation and contributes to a decrease in overall feed use efficiency.     

Milk yield and mammary growth effects due to increased milking frequency during early lactation

Increased milking frequency (IMF) at the beginning of lactation has been shown to increase milk yield not only during IMF but also after its cessation. The objectives of this experiment evaluated the effects of increased milking frequency initiated during early lactation on mammary growth and effects on milk yield (MY). Thirty-one cows were divided into treatment groups: 1) 2X: cows milked twice daily (2X) beginning at parturition (d 1), 2) IMF1: cows milked four times daily (4X) from d 1 to 21 postpartum (PP) and 3) IMF4: cows milked 2X d 1 to 3 and 4X d 4 to 21 PP. The 4X cows were milked immediately before 2X cows and again approximately 3 h later, at the end of the normal milking routine. All cows were milked 2X from d 21 to 305 postpartum. Milk yields were 34.5, 37.8 and 37.6 kg/d during wk 1 to 44 for 2X, IMF1 and IMF4, respectively. Mammary biopsies from four cows per treatment were obtained on d 7 and 14 PP to evaluate mammary cell proliferation. Tritiated-thymidine incorporation tended to increase on d 7 in IMF1 cows, and arithmetic means of the percentage of cells expressing Ki-67 proliferation antigen were consistent with a proliferative response to IMF though not significant. Blood was sampled three times per wk during the first 2 wk and then once per wk during wk 3, 4, 5, 6, 8, and 10. Plasma insulin-like growth factor-1 (IGF-1) averaged 20.1 ng/ml in IMF cows vs. 24.2 in 2X but was not accompanied by a change in bST. Prolactin was also not affected by treatment. Neither milk yield nor potential effects on mammary cell proliferation were correlated with systemic IGF-1. Implementing an IMF routine increases MY during treatment and elicits a carryover effect on the remainder of lactation. Milk yield responses after an IMF routine may be the result of increased mammary cell proliferation.     

Regional accretion of gelatinase B in mammary gland during gradual and acute involution of dairy animals

The level of gelatinases in surrounding body fluids of actively remodelling tissue is indicative of basement membrane and extracellular matrix degradation under various physiological and pathological circumstances. To elucidate the association of gelatinase with mammary tissue remodelling during gradual or acute involution, in the first trial, goats milked twice daily (lactation) and goats receiving decreased milking frequency (involution) served to provide a total of 12 milk samples and 11 mammary secretion samples, respectively. In the second trial, 6 cows served to provide samples of dry secretion in 3 consecutive weeks immediately following milk stasis. Gelatin zymography was applied for gelatinase phenotyping and quantification on milk, plasma and the degranulation medium/lysate of milk somatic cells. Results indicated that the most prevalent gelatinase subtype switched from gelatinase A in milk to gelatinase B in involution secretion. Mammary secretion of goats during involution contained marginally higher protein level, significantly lower casein ratio and greater specific capacity of gelatinase B compared with those of milk during lactation. Specific capacities of gelatinases A and B in plasma of goats were similar during lactation and involution, while gelatinase B capacity in degranulation medium/lysates based on unit number of goat somatic cell was significantly higher during involution than during lactation. Milk stasis of cows induced a significant increase in specific capacity of gelatinase B, but not gelatinase A, of dry secretion up to the third week. Results of both trials agree that regional selective accretion of gelatinase B in milk might have played a role in mammary tissue remodelling during involution induced by either decreasing milking frequency or milk stasis. It is suggested that infiltrated polymorphonuclear neutrophils are one of the potential contributors responsible for the accumulation of gelatinase B during involution.     

Lactoferrin concentration during involution of the bovine mammary gland.

Electroimmunodiffusion assay was used to quantitate changes in lactoferrin concentration in mammary secretions during involution of the bovine mammary gland. Concentration of lactoferrin began to increase 2 to 4 days after cessation of regular milking and continued to increase linearly at a rate of 1.15 mg/ml per day as a result of increased net synthesis of lactoferrin during the first 14 to 21 days of involution. Maximum lactoferrin concentration (approximately 20 mg/ml) was attained after 3 to 4 wk of involution. These changes represent a 100-fold increase in lactoferrin concentration over that in normal milk. Maximum lactoferrin concentration was variable between cows. In some cows, the concentration of lactoferrin plateaued at less than 10 mg/ml after 10 days of involution. In others, much higher lactoferrin concentrations of 75 to 100 mg/ml were measured. Lactoferrin concentration decreased markedly prior to parturition and onset of lactation. The increase in lactoferrin concentration during mammary gland involution appeared to be related closely to the process of involution.     

Amplifying local serotonin signaling prior to dry-off hastens mammary gland involution and redevelopment in dairy cows

The monoamine serotonin (5-hydroxytryptamine, 5-HT) has been reported to inhibit milk protein gene expression and increase mammary epithelial cell (MEC) tight junction permeability after milk stasis. We hypothesized that increasing serotonin synthesis and signaling within the mammary epithelium before milk stasis would increase systemic and local involution markers, and downregulate the expression of milk protein and tight junction during involution, leading to more efficient tissue growth during the redevelopment phase. Herein, we examined the outcomes of increasing local mammary 5-HT synthesis before milk stasis on involution biomarkers, mammary gland microstructure, and gene and protein expression during the dry period. Multiparous Holstein cows were administered intramammary infusions (via the teat canal) of sterile water (CON, 4 mL/teat, n = 7) or 5-hydroxy-l-tryptophan (5-HTP, serotonin precursor, 20 mg/teat, n = 7) once daily for 5 d before dry-off (d 0). Blood, milk, and mammary secretions were collected and analyzed for components and metabolites. Mammary secretions were collected 12 h after the last milking and on d 1 to 4 during the dry period at 1200 h. Mammary gland biopsies were performed on d 4 (i.e., involution phase) and d 36 (i.e., redevelopment phase) of the dry period for histological and molecular evaluation. Milk protein and tight junction gene expression was quantified via real-time PCR. Hematoxylin and eosin staining, immunohistochemistry (Ki67), and immunofluorescence (serotonin, cleaved caspase 3) were performed to visualize tissue microstructure and to quantify serotonin intensity and cell turnover. Data were analyzed in SAS (SAS Institute Inc.) using 2-way ANOVA. After d 0, mammary secretions of 5-HTP cows had increased concentrations of 5-HT, lactoferrin, and bovine serum albumin. On d 1, 5-HTP cows had greater α-lactalbumin concentrations in plasma relative to CON. Serotonin intensity was increased in the mammary tissue of 5-HTP cows on d 4, relative to CON. On d 4, milk protein and tight junction gene expression was downregulated, MEC number was reduced, and cleaved caspase 3 protein was greater in mammary tissue of 5-HTP cows, relative to CON. On d 36, milk protein genes were upregulated, and the lumen:outer alveolar area and Ki67-positive cells were increased in the mammary tissue of 5-HTP cows, relative to CON. Amplifying serotonin signaling in the mammary epithelium before milk stasis at dry-off achieves greater apoptosis, leading to a reduction in MEC, allowing for greater cell proliferation, which results in more MEC during the redevelopment phase preceding the onset of lactation.     

Suppression of mitogenic response of peripheral blood mononuclear cells by bovine mammary secretions

Effects of bovine mammary secretions collected at different stages of the lactation cycle on blood mononuclear cell response to mitogens were evaluated. Mammary secretion skims and wheys collected 7 and 28 d following cessation of milking, at parturition, and during early lactation were used. Colostrum and mammary secretions obtained 7 d after milk cessation were associated with greatest inhibition of mononuclear cell blastogenesis. Milk collected during early lactation caused the least inhibition. Mammary secretion wheys caused greater inhibition of blastogenesis than skims. Dilution of mammary secretions reduced blastogenic inhibition. Phytohemagglutinin-stimulated mononuclear cells were less inhibited by mammary secretion than Concanavalin A-stimulated cells. Suppression of mononuclear cell activity, particularly during early involution and at parturition, may influence susceptibility of the bovine mammary gland to new intramammary infections during physiological transitions of the udder.     

Thymidine incorporation by lactating mammary epithelium during compensatory mammary growth in beef cattle

Ten Hereford cows, 100 d into first lactation, were assigned to treatment or control groups to study compensatory growth of mammary glands. The right udder half of treatment cows was covered to prevent suckling by the calf, whereas control cows were suckled on all quarters. Milk production was estimated the day treatment began and 4 d later by machine milking following removal of calves for 12 h and i.v. injection of oxytocin. Five to 7 d after beginning treatment, cows were killed and mammary tissue was obtained from three regions within left and right glands for in vitro incubation with [3H]thymidine. Deoxyribonucleic acid of lactating udder halves did not increase in response to treatment although RNA: DNA ratio and milk production tended to increase. Incorporation of [3H]thymidine was greater in lactating quarters of treated cows than control cows (35,000 vs. 19,000 cpm/mg of DNA) with greatest incorporation in the basal regions of each gland. Furthermore, greatest incorporation of [3H]thymidine occurred in non-suckled glands. Autoradiographic analyses confirmed incorporation data and indicated that 81% of proliferating cells were epithelial. Data suggest that proliferation of mammary epithelial cells, within both the lactating and nonlactating glands, occurred in response to milk stasis.     

Hot topic: effects of frequent milking in early lactation on milk yield and udder health

A field study was conducted to evaluate the influence of milking frequency (3 or 6 times/d [3x or 6x, respectively]) during the initial 21 d of lactation on milk and milk component yield and mammary gland health as indicated by somatic cell count. During 2 seasons, spring and fall, multiparous cows were milked 6 times/d until d 21 of lactation and then returned to the 3 times/d frequency for the remainder of lactation (6x; n = 9). Multiparous cows milked 3 times/d from the beginning of lactation served as a control group (3x; n = 17). With the exception of milking frequency, all other aspects of management, including housing, milk harvesting, and feeding, were identical between the groups and were consistent with industry norms. Retrospective analysis of Dairy Herd Improvement Association records was used to evaluate milk yield, milk component yield, and somatic cell scores. As expected, 6x cows produced more milk on the first test day than 3x cows. Compared with 3x cows, higher milk yields persisted for 6x cows from test day 2 through 6, indicating a persistent effect of early lactation milking frequency on milk yield potential for that lactation. Milk component yield followed a similar pattern: 6x cows produced significantly more protein, fat, and total solids than did control cows throughout the study. With regard to udder health, 6x cows had lower somatic cell counts at the first test day relative to 3x cows and had reduced somatic cell scores for the first 3 mo of lactation, which suggests that early lactation milking frequency influences the mammary gland capacity to resist infection in addition to improving milk production efficiency.     

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.     

The milk yield response to frequent milking in early lactation of dairy cows is locally regulated

Frequent milking during early lactation of dairy cows increases milk production throughout lactation; however, whether this response is regulated systemically via lactogenic hormones, locally in the mammary gland, or both is unknown. We hypothesized that the effects of frequent milking on milk production during early lactation are regulated via local mechanisms. Ten multiparous cows were assigned at parturition to unilateral frequent milking [UFM; twice daily milking of the left udder half (2×), or 4 times daily milking of the right udder half (4×)] for d 1 to 21 of lactation. After treatment, cows were milked twice daily for the remainder of lactation. At the first milking after calving, milk yield from individual quarters was measured to verify that udder halves produced equal amounts of milk prior to treatment. Thereafter, individual quarters were milked on d 3 and 7, weekly for the first 5 wk of lactation, and once every 3 mo for the remainder of lactation. During UFM, cows produced 3.9 ± 0.7 kg/d more from the side milked 4× than the side milked 2×. Upon cessation of treatment, milk production from the side milked 4× decreased, but remained at 1.8 ± 0.5 kg/d more than the side milked 2× for the remainder of lactation. After milk yield was corrected to the equivalent of a whole-udder basis, acute milk yield responses to frequent milking were found to be consistent with previous reports. Moreover, we observed greater persistency in the milk yield response, which lasted throughout lactation. We conclude that both immediate and persistent effects on milk production of frequent milking during early lactation are regulated at the level of the mammary gland. Our results demonstrate that UFM is a valid and efficient model for investigating the effects of frequent milking during early lactation in dairy cows.