Effect of eprinomectin treatment on milk yield and quality in dairy cows in South Tyrol, Italy

The effect of treatment with eprinomectin on milk yield, milk composition and somatic cell counts (SCCs) was studied in 105 dairy cows located on seven farms in South Tyrol, Italy. On each farm, half of the animals were treated with eprinomectin and the other half were used as an untreated control group. Three test day records per animal were obtained before treatment (days -117, -75 and -33) and another three test day records were obtained after treatment (days 22, 62 and 131). Test day records comprised milk yield, milk composition, SCC and days in milk. On the day of treatment, blood samples and faecal samples were taken for parasitological analysis. Cows with positive faecal egg counts yielded less milk. A significant effect of eprinomectin on milk yield was observed after treatment and was most pronounced on the second and the third test days after treatment (+1.90 kg [P=0.002] and +2.63 kg [P<0.001], respectively). Furthermore, a significant decrease in SCC was observed on the second test day after treatment.

A case-control study to estimate the effects of acute clinical infection with the Schmallenberg virus on milk yield, fertility and veterinary costs in Swiss dairy herds.

Schmallenberg virus (SBV) was first detected in Switzerland in July 2012 and many Swiss dairy farmers reported acute clinical signs in dairy cattle during the spread of the virus until December 2012. The objectives of the present study were to investigate the effects of an acute infection with SBV on milk yield, fertility and veterinary costs in dairy farms with clinical signs of SBV infection (case farms), and to compare those farms to a matched control group of dairy farms in which cattle did not show clinical signs of SBV infection. Herd size was significantly (p<0.001) larger in case farms (33 cows, n=77) than in control farms (25 cows, n=84). Within case herds, 14.8% (median) of the cows showed acute clinical signs. Managers from case farms indicated to have observed a higher abortion rate during the year with SBV (6.5%) than in the previous year (3.7%). Analysis of fertility parameters based on veterinary bills and data from the breeding associations showed no significant differences between case and control farms. The general veterinary costs per cow from July to December 2012 were significantly higher (p=0.02) in case (CHF 19.80; EUR 16.50) than in control farms (CHF 15.90; EUR 13.25). No differences in milk yield were found between groups, but there was a significant decrease in milk production in case farms in the second half year in 2012 compared to the same period in 2011 (p<0.001) and 2013 (p=0.009). The average daily milk yield per cow (both groups together) was +0.73kg higher (p=0.03) in the second half year 2011 and +0.52kg (p=0.12) in the second half year 2013 compared to the same half year 2012. Fifty-seven percent of the cows with acute clinical signs (n=461) were treated by a veterinarian. The average calculated loss after SBV infection for a standardized farm was CHF 1606 (EUR 1338), which can be considered as low at the national level, but the losses were subject to great fluctuations between farms, so that individual farms could have very high losses (>CHF 10,000, EUR 8333).

Best combination of pre-stimulation and latency period duration before cluster attachment for efficient oxytocin release and milk ejection in cows with low to high udder-filling levels

Experiments were designed to investigate the suitability of a combination of a short manual teat stimulation with a short latency period before teat cup attachment to induce and maintain oxytocin release and milk ejection without interruption. In Experiment 1, seven dairy cows in mid lactation were manually pre-stimulated for 15, 30 or 45 s, followed by either 30 s or 45 s of latency period. It was shown that all treatments induced a similar release of oxytocin without interruption until the end of milking. In particular, the latency period of up to 45 s did not cause a transient decrease of oxytocin concentration. In Experiment 2, milking characteristics were recorded in seven cows each in early, mid, and late lactation, respectively. Because the course of milk ejection depends mainly on the degree of udder filling, individual milkings were classified based on the actual degree of udder filling which differs between lactational stages but also between morning and evening milkings. All animals underwent twelve different udder preparation treatments, i.e. 15, 30, or 45 s of pre-stimulation followed by latency periods of 0, 30, 45, or 60 s. Milking characteristics were recorded. Total milk yield, main milking time and average milk flow rate did not differ between treatments if the degree of udder filling at the start of milking was >40% of the maximum storage capacity. However, if the udder filling was <40%, main milking time was decreased with the duration of a latency period up to 45 s, independent of duration of pre-stimulation. Average milk flow at an udder filling of <40% was highest after a pre-stimulation of 45 s followed by a latency period of another 45 s. In contrast, average milk flow reached its lowest values at a pre-stimulation of 15 s without additional latency period. However, average milk flow after a 15-s pre-stimulation increased with increasing latency period. In conclusion, a very short pre-stimulation when followed by a latency period up to 45 s before teat cup attachment remains a suitable alternative for continuous stimulation to induce milk ejection.

Milk flow-dependent vacuum loss in high-line milking systems: effects on milking characteristics and teat tissue condition

To study the effects of a milking system that partially compensates for milk flow-dependent vacuum loss compared with a standard (high-line) milking unit in a tie-stall barn, milk flow and vacuum patterns were recorded in 10 cows during machine milking with 2 milking systems in a crossover design for 7 d each. Before and after each treatment period postmilking teat condition was recorded by ultrasound cross-sectioning. Additionally, 2 methods to measure teat tissue condition were compared: longitudinal teat ultrasound cross-sectioning and teat tissue density measurements with the spring-loaded caliper (cutimeter method). The partial compensation of milk flow-dependent vacuum loss caused an elevation of the peak flow rate (4.74+/-0.08 vs. 4.29+/-0.07 kg/min) and a shorter duration of plateau (1.57+/-0.06 vs. 1.96+/-0.07 min) compared with the standard milking system. Total milk yield, duration of incline and decline of milk flow, average milk flow, time until peak flow rate, main milking time, and total milking time did not differ between treatments (overall means: 13.75+/-0.17 kg; 0.65+/-0.01 min; 2.88+/-0.09 min; 2.82+/-0.05 kg/min; 1.65+/-0.03 min; 5.23+/-0.09 min, and 5.30+/-0.10 min, respectively). The vacuum drop in the short milk tube during periods of high milk flow was less in the compensating vacuum than in the standard milking system (11+/-1.1 vs. 15+/-0.7 kPa). Teat measures as determined by ultrasound remained unchanged over the entire experimental period with both milking systems. Postmilking teat tissue measures including their recovery within 20 min after the end of milking show a correlation (0.85 and 0.71, respectively) between the methods used (ultrasound and cutimeter method). In conclusion, a more constant vacuum at the teat tip (within the short milk tube) during periods of high milk flow affected milk flow patterns, mainly increasing peak flow rate. However, the reduced vacuum loss did not increase the overall speed of milking. In addition, effects of higher vacuum stability on teat condition and udder health were not obvious.

Differences in milk production, glucose metabolism, and carcass composition of 2 Charolais x Holstein F2 families derived from reciprocal paternal and maternal grandsire crosses

Two F(2) Charolais x German Holstein families comprising full and half sibs share identical but reciprocal paternal and maternal Charolais grandfathers differ in milk production. We hypothesized that differences in milk production were related to differences in nutritional partitioning revealed by glucose metabolism and carcass composition. In 18F(2) cows originating from mating Charolais bulls to German Holstein cows and a following intercross of the F(1) individuals (n=9 each for family Ab and Ba; capital letters indicate the paternal and lowercase letter the maternal grandsire), glucose tolerance tests were performed at 10 d before calving and 30 and 93 d in milk (DIM) during second lactation. Glucose half-time as well as areas under the concentration curve for plasma glucose and insulin were calculated. At 94 DIM cows were infused intravenously with 18.3 micromol of d-[U-(13)C(6)]glucose/kg(0.75) of BW, and blood samples were taken to measure rate of glucose appearance and glucose oxidation as well as plasma concentrations of metabolites and hormones. Cows were slaughtered at 100 DIM and carcass size and composition was evaluated. Liver samples were taken to measure glycogen and fat content, gene expression levels, and enzyme activities of pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and glucose 6-phosphatase as well as gene expression of glucose transporter 2. Milk yield was higher and milk protein content at 30 DIM was lower in Ba than in Ab cows. Glucose half-life was higher but insulin secretion after glucose challenge was lower in Ba than in Ab cows. Cows of Ab showed higher glucose oxidation, and plasma concentrations at 94 DIM were lower for glucose and insulin, whereas beta-hydroxybutyrate was higher in Ba cows. Hepatic gene expression of pyruvate carboxylase, glucose 6-phosphatase, and glucose transporter 2 were higher whereas phosphoenolpyruvate carboxykinase activities were lower in Ba than in Ab cows. Carcass weight as well as fat content of the carcass were higher in Ab than in Ba cows, whereas mammary gland mass was lower in Ab than in Ba cows. Fat classification indicated leaner carcass composition in Ba than in Ab cows. In conclusion, the 2 families showed remarkable differences in milk production that were accompanied by changes in glucose metabolism and body composition, indicating capacity for milk production as main metabolic driving force. Sex chromosomal effects provide an important regulatory mechanism for milk performance and nutrient partitioning that requires further investigation.

Milk cortisol concentration in automatic milking systems compared with auto-tandem milking parlors

Milk cortisol concentration was determined under routine management conditions on 4 farms with an auto-tandem milking parlor and 8 farms with 1 of 2 automatic milking systems (AMS). One of the AMS was a partially forced (AMSp) system, and the other was a free cow traffic (AMSf) system. Milk samples were collected for all the cows on a given farm (20 to 54 cows) for at least 1 d. Behavioral observations were made during the milking process for a subset of 16 to 20 cows per farm. Milk cortisol concentration was evaluated by milking system, time of day, behavior during milking, daily milk yield, and somatic cell count using linear mixed-effects models. Milk cortisol did not differ between systems (AMSp: 1.15 +/- 0.07; AMSf: 1.02 +/- 0.12; auto-tandem parlor: 1.01 +/- 0.16 nmol/L). Cortisol concentrations were lower in evening than in morning milkings (1.01 +/- 0.12 vs. 1.24 +/- 0.13 nmol/L). The daily periodicity of cortisol concentration was characterized by an early morning peak and a late afternoon elevation in AMSp. A bimodal pattern was not evident in AMSf. Finally, milk cortisol decreased by a factor of 0.915 in milking parlors, by 0.998 in AMSp, and increased by a factor of 1.161 in AMSf for each unit of ln(somatic cell count/1,000). We conclude that milking cows in milking parlors or AMS does not result in relevant stress differences as measured by milk cortisol concentrations. The biological relevance of the difference regarding the daily periodicity of milk cortisol concentrations observed between the AMSp and AMSf needs further investigation.

Incontinentia lactis: physiology and anatomy conducive to milk leakage in dairy cows

Incontinentia lactis is a possible predisposing factor for an elevated level of intramammary infection. The goal of the present study was to investigate possible causes of incontinentia lactis in dairy cows. Two farms that differed in breed composition, but that had similar average milk yields were studied: herd A, 28 kg/d, 31 Red Holstein cows; and herd B, 26 kg/d, 16 Brown Swiss cows. Herd A was classified into 2 groups: incontinentia lactis (ILA group) and control, whereas herd B was exclusively a control herd. Milk samples that represented foremilk and the main milk fraction were collected during 4 milking sessions. In addition, milk leakage samples from the ILA group were collected at different time intervals from 0 to 5 h before milking. Measurements of the teat, milk flow, fractions of cisternal and alveolar milk, intramammary pressure, and blood oxytocin pattern also were obtained. The ILA cows did not have differences in fat content between milk leakage and cisternal milk fraction. Milk fat content, however, increased during milking in response to continuous milk ejection (1.95, 1.99, and 4.61% for milk leakage, cisternal, and main milk samples, respectively). Teat canals were 9% shorter in the ILA cows, which showed greater milk yield, peak, and average flow rates. Quarter cisternal milk yield of ILA cows tended to be greater (0.50 vs. 0.23 and 0.28 kg for ILA and controls from herds A and B, respectively), whereas percentages of cistern milk and alveolar milk did not differ from controls. The greater pressure in the ILA group, both before and after manual udder stimulation (ILA: 4.0 and 6.4 kPa; control: 2.0 and 5.0 kPa, respectively), could be an important cause for the leakage. Nevertheless, the increase in IMP that occurred after udder preparation affirms that milk ejection occurred in response to the tactile teat stimulation, but not before the onset of leakage. Blood oxytocin concentration in ILA cows was low until the start of udder preparation and increased in response to the milking stimulus (reaffirming the hypothesis that milk leakage occurred in the absence of milk ejection). In conclusion, milk losses by leakage are likely due to the large amount of cisternal milk, which creates pressure and causes leakage, in the absence of milk ejection.

Long-term elevation of β-hydroxybutyrate in dairy cows through infusion: effects on feed intake, milk production, and metabolism.

Elevation of ketone bodies in dairy cows frequently occurs in early lactation, usually concomitantly with a lack of energy and glucose. The objective of this study was to induce an elevated plasma β-hydroxybutyrate (BHBA) concentration over 48 h in mid-lactating dairy cows (i.e., during a period of positive energy balance and normal glucose plasma concentrations). Effects of BHBA infusion on feed intake, metabolism, and performance were investigated. Thirteen cows were randomly assigned to 1 of 2 infusion groups, including an intravenous infusion with Na-dl-β-OH-butyrate (1.7 mol/L) to achieve a plasma concentration of 1.5 to 2.0 mmol/L of BHBA (HyperB; n=5), or an infusion of 0.9% saline solution (control; n=8). Blood was sampled before and hourly during the 48 h of infusion. In the liver, mRNA transcripts related to gluconeogenesis (pyruvate carboxylase, glucose 6-phosphatase, mitochondrial phosphoenolpyruvate carboxykinase), phosphofructokinase, pyruvate dehydrogenase complex, and fatty acid synthesis (acetyl-coenzyme A carboxylase, fatty acid synthase) were measured by real-time PCR. Glyceraldehyde-3-phosphate dehydrogenase and ubiquitin were used as housekeeping genes. Changes (difference between before and after 48-h infusion) during the infusion period were evaluated by ANOVA with treatment as fixed effect, and area under the curve of variables was calculated on the second day of experiment. The plasma BHBA concentration in HyperB cows was 1.74 ± 0.02 mmol/L (mean ± SE) compared with 0.59 ± 0.02 mmol/L for control cows. The change in feed intake, milk yield, and energy corrected milk did not differ between the 2 experimental groups. Infusion of BHBA reduced the plasma glucose concentration (3.47 ± 0.11 mmol/L) in HyperB compared with control cows (4.11 ± 0.08 mmol/L). Plasma glucagon concentration in HyperB was lower than the control group. All other variables measured in plasma were not affected by treatment. In the liver, changes in mRNA abundance for the selected genes were similar between 2 groups. Results demonstrate that intravenous infusion of BHBA decreased plasma glucose concentration in dairy cows, but this decrease could not be explained by alterations in insulin concentrations or key enzymes related to gluconeogenesis. Declined glucose concentration is likely functionally related to decreased plasma glucagon concentration.

Milk production during the colostral period is not related to the later lactational performance in dairy cows

In dairy cows, milk yield increases rapidly after parturition until a peak at around wk 6 of lactation. However, the description of the shape of the lactation curve is commonly based on weekly average milk yields. For a more detailed analysis of the milk production curve from the very beginning of lactation including the colostral period and the effect of colostrum yield on further lactational performance, the first 10 milkings after parturition, daily milk yields from d 1 to 28 of lactation, and the cumulative milk production on d 100 to 305 of lactation were investigated in 17 primiparous and 39 multiparous cows milked twice daily. Milk yield at the first milking after parturition (colostrum) ranged from 1.3 to 20.7kg (Δ=19.4kg) in multiparous and from 1.8 to 10.9kg in primiparous animals (Δ=9.1kg). At the tenth milking, milk production ranged from 9.2 to 21.5kg (Δ=12.3kg) in multiparous and from 7.0 to 15.2kg (Δ=8.2kg) in primiparous animals. Immediately after parturition, daily milk production increased rapidly, but after approximately 1wk in lactation, the slope of the daily milk production curve flattened and continued more linear. A nonlinear regression equation was used to determine this timely change, which occurred earlier in primiparous (d 6.9±0.3) than in multiparous cows (d 8.2±0.2). The correlation between the amount of first colostrum and milk production during further lactation decreased already from 0.47 on d 5 to 0.32 on d 14. In multiparous cows, the correlation between total milk production of the previous 305d standard lactation and the amount of first colostrum was not significant (correlation=0.29), whereas the correlation with the daily production increased from 0.45 on d 5 to 0.69 on d 14. However, in primiparous animals, correlations between first-colostrum yield and daily milk yields up to d 28 of lactation were not significant, possibly due to the smaller sample size compared with multiparous animals. First-colostrum yield and cumulative milk production of 100, 200, and 305 lactation days were not significantly correlated in multiparous and primiparous cows. In conclusion, the milk production during the first few milkings is widely independent from the overall production level of a cow. Potentially, genetic selection toward lower milk yield during the very first days after parturition at a simultaneously high lactational performance may be a tool to ensure sufficient colostrum quality and to reduce the metabolic load around parturition.

Short communication: Circulating and milk adiponectin change differently during energy deficiency at different stages of lactation in dairy cows

Adiponectin, one of the most abundant adipokines in circulation, is known for its role in regulation of body metabolism. The aim of this study was to evaluate the effects of a negative energy balance (NEB) at 2 stages of lactation (lactational NEB at the onset of lactation and an induced NEB by feed restriction near 100 d of lactation) on circulating adiponectin concentrations. We also investigated the effect of feed restriction on adiponectin concentrations in milk and the relationships of blood and milk adiponectin with selected plasma or milk variables and with measures of body condition. Plasma adiponectin was measured in 50 multiparous Holstein dairy cows throughout 3 experimental periods [i.e., period 1=3 wk antepartum up to 12 wk postpartum, period 2=3 wk of feed restriction starting at around 100 d in milk with a control (n=25) and feed-restricted group (50% of energy requirements; n=25), and period 3=subsequent realimentation period for 8 wk]. Milk adiponectin was investigated among 21 multiparous cows at wk 2 and wk 12 of period 1 and wk 2 of period 2. Adiponectin concentrations in plasma and skim milk were measured using an in-house ELISA specific for bovine adiponectin. Major changes in circulating adiponectin concentrations were observed during the periparturient period, whereas energy deficiency during established lactation at around 100 d in milk and subsequent refeeding did not affect plasma adiponectin. Together with lower adiponectin concentrations in milk (µg/mL), the reduction in milk yield led to decreased adiponectin secretion via milk (mg/d) at the second week of feed restriction. Irrespective of time and treatment, milk adiponectin represented about 0.002% of total milk protein. Mean adiponectin concentrations in milk (0.61 ± 0.03 µg/mL) were about 92% lower than the mean plasma adiponectin concentrations (32.1 ± 1.0 µg/mL). The proportion of the steady-state plasma adiponectin pool secreted daily via milk was 2.7%. In view of the similar extent of NEB in both periods of energy deficiency, decreasing adiponectin concentrations seems important for accomplishing the adaptation to the rapidly increasing metabolic rates in early lactation, whereas the lipolytic reaction toward feed restriction-induced NEB during established lactation seems to occur largely independent of changes in circulating adiponectin.

Effects of long-term feeding of genetically modified corn (event MON810) on the performance of lactating dairy cows

A long-term study over 25 months was conducted to evaluate the effects of genetically modified corn on performance of lactating dairy cows. Thirty-six dairy cows were assigned to two feeding groups and fed with diets based on whole-crop silage, kernels and whole-crop cobs from Bt-corn (Bt-MON810) or its isogenic not genetically modified counterpart (CON) as main components. The study included two consecutive lactations. There were no differences in the chemical composition and estimated net energy content of Bt-MON810 and CON corn components and diets. CON feed samples were negative for the presence of Cry1Ab protein, while in Bt-MON810 feed samples the Cry1Ab protein was detected. Cows fed Bt-MON810 corn had a daily Cry1Ab protein intake of 6.0 mg in the first lactation and 6.1 mg in the second lactation of the trial. Dry matter intake (DMI) was 18.8 and 20.7 kg/cow per day in the first and the second lactation of the trial, with no treatment differences. Similarly, milk yield (23.8 and 29.0 kg/cow per day in the first and the second lactation of the trial) was not affected by dietary treatment. There were no consistent effects of feeding MON810 or its isogenic CON on milk composition or body condition. Thus, the present long-term study demonstrated the compositional and nutritional equivalence of Bt-MON810 and its isogenic CON.

Comparison of the effect of a CIDR-Select synch versus a long-term CIDR based AI protocol on reproductive performance in multiparous dairy cows in Swiss dairy farms

Background Synchronization programs have become standard in the dairy industry in many countries. In Switzerland, these programs are not routinely used for groups of cows, but predominantly as a therapy for individual problem cows. The objective of this study was to compare the effect of a CIDR-Select Synch and a 12-d CIDR protocol on the pregnancy rate in healthy, multiparous dairy cows in Swiss dairy farms. Methods Cows (N = 508) were randomly assigned to CIDR-Select Synch (N = 262) or 12-d CIDR (N = 246) protocols. Cows in the CIDR-Select Synch group received a CIDR and 2.5 ml of buserelin i.m. on d 0. On d 7, the CIDR insert was removed and 5 ml of dinoprost was administered i.m.. Cows in the 12-d CIDR group received the CIDR on d 0 and it was removed on d 12 (the routine CIDR protocol in Swiss dairies). On d 0 a milk sample for progesterone analysis was taken. Cows were inseminated upon observed estrus. Pregnancy was determined at or more than 35 days after artificial insemination. As a first step, the two groups were compared as to indication for treatment, breed, stud book, stall, pasture, and farmer's business using chi square tests or Fisher's exact test. Furthermore, groups were compared as to age, DIM, number of AI's, number of cows per farm, and yearly milk yield per cow using nonparametric ANOVA. A multiple logistic model was used to relate the success of the protocols to all of the available factors; in particular treatment (CIDR-Select Synch/12-d CIDR), milk progesterone value, age, DIM, previous treatment of the uterus, previous gynecological treatment, and number of preceding inseminations. Results The pregnancy rate was higher in cows following the CIDR-Select Synch compared to the 12-d CIDR protocol (50.4% vs. 22.4%; P < 0.0001). Conclusion The CIDR-Select Synch protocol may be highly recommended for multiparous dairy cows. The reduced time span of the progesterone insert decreased the number of days open, improved the pregnancy rate compared to the 12-d CIDR protocol and the cows did not to have to be handled more often.

Rumen-protected choline supplementation in periparturient dairy goats: effects on liver and mammary gland

The current study investigated the effects of supplementing rumen-protected choline (RPC) on metabolic profile, selected liver constituents and transcript levels of selected enzymes, transcription factors and nuclear receptors involved in mammary lipid metabolism in dairy goats. Eight healthy lactating goats were studied: four received no choline supplementation (CTR group) and four received 4g RPC chloride/day (RPC group). The treatment was administered individually starting 4 weeks before expected kidding and continuing for 4 weeks after parturition. In the first month of lactation, milk yield and composition were measured weekly. On days 7, 14, 21 and 27 of lactation, blood samples were collected and analysed for glucose, beta-hydroxybutyrate, non-esterified fatty acids and cholesterol. On day 28 of lactation, samples of liver and mammary gland tissue were obtained. Liver tissue was analysed for total lipid and DNA content; mammary tissue was analysed for transcripts of lipoprotein lipase (LPL), fatty acid synthase (FAS), sterol regulatory binding proteins 1 and 2, peroxisome proliferator-activated receptor gamma and liver X receptor alpha. Milk yield was very similar in the two groups, but R PC goats had lower (P < 0.05) plasma beta-hydroxybutyrate. The total lipid content of liver was unaffected (P = 0.890), but the total lipid/DNA ratio was lower (both P < 0.05) in RPC than CTR animals. Choline had no effect on the expression of the mammary gland transcripts involved in lipid metabolism. The current plasma and liver data indicate that choline has a positive effect on liver lipid metabolism, whereas it appears to have little effect on transcript levels in mammary gland of various proteins involved in lipid metabolism. Nevertheless, the current results were obtained from a limited number of animals, and choline requirement and function in lactating dairy ruminants deserve further investigation.

Effects of nutrient restriction on mammary cell turnover and mammary gland remodeling in lactating dairy cows

The aim of this study was to investigate the effects of a severe nutrient restriction on mammary tissue morphology and remodeling, mammary epithelial cell (MEC) turnover and activity, and hormonal status in lactating dairy cows. We used 16 Holstein x Normande crossbred dairy cows, divided into 2 groups submitted to different feeding levels (basal and restricted) from 2 wk before calving to wk 11 postpartum. Restricted-diet cows had lower 11-wk average daily milk yield from calving to slaughter than did basal-diet cows (20.5 vs. 33.5 kg/d). Feed restriction decreased milk fat, protein, and lactose yields. Restriction also led to lower plasma insulin-like growth factor 1 and higher growth hormone concentrations. Restricted-diet cows had lighter mammary glands than did basal-diet cows. The total amount of DNA in the mammary gland and the size of the mammary acini were smaller in the restricted-diet group. Feed restriction had no significant effect on MEC proliferation at the time of slaughter but led to a higher level of apoptosis in the mammary gland. Gelatin zymography highlighted remodeling of the mammary extracellular matrix in restricted-diet cows. Udders from restricted-diet cows showed lower transcript expression of alpha-lactalbumin and kappa-casein. In conclusion, nutrient restriction resulted in lower milk yield in lactating dairy cows, partly due to modulation of MEC activity and a lower number of mammary cells. An association was found between feed restriction-induced changes in the growth hormone-insulin-like growth factor-1 axis and mammary epithelial cell dynamics.