ABSTRACT: Plants’ physiology changes through the day because photoassimilates can increase water-soluble carbohydrate concentration in the afternoon compared to the morning. This study evaluated the harvest time effect on whole-plant corn silage morphological composition, particle size, fermentation profile, chemical composition, in vitro degradation, and estimated milk yield. A two-year agronomic assay was performed in a completely random design, and one experimental silo was produced by each parcel (n = 16). The afternoon harvest increased (P < 0.01) dry matter content compared to the morning harvest. Harvest time did not affect (P ≥ 0.32) corn grain, stalk, leaf proportion, and silage particle size. However, the morning harvest increased dry matter recovery (P = 0.01) and had no effect (P ≥ 0.10) on silage pH and concentrations of lactic and acetic acid compared to the afternoon harvest. In addition, afternoon harvest instead of morning harvest increased (P ≤ 0.05) silage starch, water-soluble carbohydrates, acid detergent lignin, and ether extract content and dry matter in vitro degradation. Controversially, treatments showed no effect (P ≥ 0.14) on silage energy concentration, estimated energy content, and milk yield. Thus, the morning harvest produces more silage dry matter, but the afternoon harvest improves corn silage’s nutritional value with no impact on estimated milk yield. ABSTRACT Plants watersoluble water soluble wholeplant whole plant composition size profile degradation yield twoyear two year design n 16. 16 . 16) P 0.01 001 0 01 0.32 032 32 grain stalk proportion However 0.10 010 10 addition 0.05 005 05 starch carbohydrates lignin Controversially 0.14 014 14 Thus silages s 1 0.0 00 0.3 03 3 0.1 0.

RESUMO: A fisiologia das plantas muda ao longo do dia porque os fotoassimilados podem aumentar a concentração de carboidratos solúveis em água à tarde em comparação com a manhã. Este estudo teve como objetivo avaliar o efeito do horário de colheita na composição morfológica da silagem de milho de planta inteira, tamanho de partícula, perfil de fermentação, composição química, degradação in vitro e estimativa da produção de leite. Um ensaio agronômico de dois anos foi realizado em delineamento inteiramente casualizado, e um silo experimental foi produzido por cada parcela (n = 16). A colheita da tarde aumentou (P < 0,01) o teor de matéria seca em relação à colheita da manhã. A época de colheita não afetou (P ≥ 0,32) a proporção de grãos, colmos e folhas do milho e o tamanho das partículas da silagem. Entretanto, a colheita da manhã aumentou (P = 0,01) a recuperação de matéria seca e não teve efeito (P ≥ 0,10) no pH da silagem e nas concentrações de ácido láctico e acético em comparação à colheita da tarde. Além disso, a colheita da tarde, em vez da colheita da manhã, aumentou (P ≤ 0,05) o amido da silagem, os carboidratos solúveis em água, a lignina detergente ácida e o teor de extrato etéreo e a degradação in vitro da matéria seca. Controversamente, os tratamentos não mostraram efeito (P ≥ 0,14) na concentração de energia da silagem, no conteúdo energético estimado e na produção de leite. Assim, a colheita da manhã produz mais matéria seca da silagem, mas a colheita da tarde melhora o valor nutricional da silagem de milho sem impacto na produção estimada de leite. RESUMO inteira partícula fermentação química leite casualizado n 16. 16 . 16) P 0,01 001 0 01 0,32 032 32 grãos Entretanto 0,10 010 10 disso 0,05 005 05 Controversamente 0,14 014 14 Assim 1 0,0 00 0,3 03 3 0,1 0,

ABSTRACT The aim of this study was to evaluate the effects of injectable mineral and vitamin supplementation on reproductive and productive performance in grazing cows. Seventy-two cows were assigned to the following groups: (1) control (CON, n=18); (2) injectable mineral supplementation (SIM, n=18); (3) injectable vitamin supplementation (SIV, n=18); and (4) SIMV (SIM + SIV) (n=18). IM supplementation was done 20 days before calving, on the day of calving and 30 days after delivery. SIM, SIV and SIMV treatments resulted in a decreased calving interval to first artificial insemination and improved milk production. The injection of vitamins or minerals did not differ from the control group in number of assisted calving, retained placenta, interval from calving to conception and pregnancy rate according to the number of inseminations.

RESUMEN El objetivo del estudio fue evaluar los efectos de la suplementación inyectable de minerales y vitaminas sobre el desempeño reproductivo y productivo en vacas en pastoreo. Setenta y dos vacas se asignaron a los siguientes grupos: (1) control (CON, n=18); (2) suplementación inyectable de minerales (SIM, n=18); (3) suplementación inyectable de vitaminas (SIV, n=18); y (4) SIMV (SIM + SIV) (n=18). La suplementación vía IM se hizo a 20 días del preparto, el día del parto y 30 días después del parto. Los tratamientos de SIM, SIV y SIMV resultaron en una disminución del intervalo del parto hasta la primera inseminación artificial y mejora de la producción de leche. La inyección de vitaminas o minerales no difirió con el grupo control en número de partos asistidos, retenciones placentarias, intervalo desde el parto hasta la concepción y tasa de preñez según el número de inseminaciones.

ABSTRACT The chemical characteristics of Cenchrus clandestinus grass, nutritional base in dairy production systems, demand the energy supplementation. Corn grain is the most used food for this purpose, but considering its demand and prices, the aim of this study was to evaluate its partial replacement by alternative non-fibrous carbohydrates sources on methane emissions, energy and nitrogen balance and productive performance of dairy cows. Sixteen multiparous Holstein cows were fed Cenchrus clandestinus plus one of four concentrate supplements formulated with corn (Zea mays) or a partial replacement of corn with sorghum (Sorghum vulgare), cassava (Manihot esculenta) or citrus pulp (Citrus sp). Inclusion of these ingredients did not affect dry matter intake, dry matter digestibility, enteric methane emissions, energy and nitrogen balance, milk yield or composition. The results allow to conclude that these ingredients can partially replace corn in the diet of lactating dairy cows.

RESUMEN Las características químicas del pasto Cenchrus clandestinus, base alimenticia en los sistemas de producción lechera, hacen necesaria la suplementación energética. El grano de maíz es el alimento más empleado para este propósito, pero dada su demanda y precio, el objetivo de este trabajo fue evaluar su reemplazo parcial por otras fuentes de carbohidratos no fibrosos sobre la emisión de metano, el balance energético-nitrogenado y el desempeño productivo de vacas lecheras. Dieciséis vacas Holstein recibieron Cenchrus clandestinus y uno de cuatro concentrados formulados con maíz (Zea mays) y sorgo (Sorghum vulgare), yuca (Manihot esculenta) o pulpa cítrica (Citrus sp) en reemplazo parcial del maíz. La inclusión de estos ingredientes no alteró el consumo de materia seca ni su digestibilidad, producción de metano, balance energético-nitrogenado, producción de leche o su composición. Los resultados permiten concluir que esos ingredientes pueden reemplazar parcialmente al maíz en la dieta de vacas lecheras.

ABSTRACT The goal of this investigation was to study the influence of different values of Temperature-Humidity index (THI) on the duration of lying down and feed consumption, productivity, and heat production by dairy cows in two variants of feedlots (with and without shelters). The study was conducted from February 2007 to early August 2021 in the central part of Ukraine (Kyiv region) in different periods of THI. This index was divided into three categories: 1) 66-71: normal (14 days); 2) 72-79: alert (11 days); 3) ≥ 80: dangerous (9 days). Two variants of feedlots were selected: Open feedlot with shelters and open feedlot without shelters. The largest increase in values of THI affecting the cows was observed in open feedlots without shelters. There, in alert and danger periods duration of feed consumption decreased by 8.0 and 23.1 min, lying down by 17 and 38 min, productivity by 2.3 kg (or 8.77%) and 3.6 kg (or 13.74%), energy consumption by 4.7 and 9.6 MJ, respectively, in comparison to normal period.

RESUMEN El objetivo del estudio fue evaluar la influencia de diferentes valores de Índice temperatura-humedad (IHT) sobre el tiempo de reposo y el consumo de alimento, la productividad y la producción de calor de las vacas lecheras en dos variantes de feedlots (con y sin refugio). El estudio se llevó a cabo desde febrero de 2007 hasta principios de agosto de 2021 en la parte central de Ucrania (región de Kiev) en diferentes períodos de IHT. El índice se dividió en tres categorías: 1) 66-71: normal (14 días); 2) 72-79: alerta (11 días); 3) >80: peligroso (9 días). Se seleccionaron dos variantes de feedlots: abierto con sombra y abierto sin sombra. El mayor aumento en los valores de IHT que afectaron a las vacas se observó en los corrales de engorda abiertos sin sombras. Allí, en periodos de alerta y peligro, la duración del consumo de alimento disminuyó en 8.0 y 23.1 min, acostado en 17 y 38 min, la productividad en 2.3 kg (o 8.77%) y 3.6 kg (o 13.74%), el consumo de energía en 4.7 y 9.6 MJ, respectivamente, en comparación con el periodo normal.

ABSTRACT The effect of four harvest ages (90, 120, 150 and 180 days) on the aerial biomass yield and chemical composition of rapeseed was evaluated, as well as its use as a hay supplement for dairy cows grazing at an altitude of 3279 m. Forage yield and its chemical composition were evaluated in 16 plots, 4 per treatment, according to a randomized complete block design. The harvested rapeseed biomass was hayed and chopped to 1 cm in length, supplied daily at a rate of 3 kg per cow. Sixteen crossbred and multiparous Holstein cows were distributed in four treatments that consisted of hays made according to harvest age. Milk production per cow was recorded for six weeks. Total solids, fat, protein, and lactose were determined in the last week of the study. As rapeseed age increased, forage biomass and neutral detergent fiber (NDF) increased, and crude protein concentration decreased; however, milk production and its milk components were not affected by the supplementation of the four types of hay, except for rapeseed hay harvested at 90 days of age, which increased the milk protein content.

RESUMEN Se evaluó el efecto de cuatro edades de cosecha (90, 120, 150 y 180 días) sobre el rendimiento de biomasa aérea y composición química de la colza, así como su uso como suplemento henificado para vacas lecheras en pastoreo a 3279 msnm. El rendimiento forrajero y la composición química se evalúo en 16 parcelas, 4 por tratamiento, de acuerdo con un diseño de bloques completos al azar. La biomasa de colza cosechada fue henificada y picada a 1 cm de longitud, suministrada diariamente a razón de 3 kg por vaca. Dieciséis vacas Holstein cruzadas y multíparas se distribuyeron en cuatro tratamientos que consistieron en henos elaborados de acuerdo con la edad de cosecha. La producción de leche por vaca se registró durante seis semanas. Los sólidos totales, grasa, proteína y lactosa se determinaron en la última semana del estudio. A medida que la edad de la colza fue mayor se incrementó la biomasa forrajera y la fibra detergente neutra (FDN), y disminuyó la concentración de proteína cruda; sin embargo, la producción de leche y sus componentes lácteos no se vieron afectados por la suplementación de los cuatro tipos de heno, con excepción del heno de colza cosechada a 90 días de edad, que incrementó el contenido de proteína láctea.

ABSTRACT The interaction between pasture and supplementation in dairy production systems constitutes a very important part of the efficiency of dairy. This study evaluated the effect of the herbage mass (HM) on the milk production and solid concentration. Twenty Holstein cows were distributed into two groups, 10 assigned 2200 kg DM ha-1 (low herbage mass, LHM) and 10 with 2800 kg DM ha-1 (medium herbage mass, MHM). Herbage mass was measured above 5 cm. The experiment lasted 8 wk. The variables evaluated were DM intake (DMI), milk production and composition (fat and protein concentration). Effects of treatments on variables were evaluated using a repeated measure analysis over time. The results showed nonsignificant differences in the pasture DMI between LHM and MHM for weeks 1, 2, 3 and 5 (P > 0.05). During week 4, pasture DMI was 3 kg greater for LHM than MHM (P < 0.05). The milk production did not differ between treatments per week, but the average was 2.4 kg greater for LHM compared to MHM (P < 0.05). In conclusion, changes in the pasture availability increased milk production at LHM, but not enough to cause changes in solids concentration. This clearly shows that, LHM can increase milk and solids production.

ABSTRACT The objective was to evaluate the effect of intensifying dairy systems on the uptake and return of nutrients in pastures. The experiment was conducted using four milk production systems on Mombasa grass pastures in the humid tropics, during the rainy season in 2009. This was a 2 x 2 factorial (two nitrogen fertilization levels and concentrate supplement or not for grazing animals) completely randomized design with four replications (paddocks). Nitrogen levels corresponded to 400 and 800 kg. ha-1.year-1, and supplementation was given to only two out of four groups of animals with milk yield above 11 L. day-1. Pastures fertilized with the highest nitrogen level had higher contents of macronutrients in plant tissues and the litter but resulted in lower concentrations of N and Ca in feces. The uptake of macronutrients per grazing cycle was also higher in these pastures. The supplementation caused a decreasing effect on the content of N in dead pasture material, P in litter, and Ca, Mg, and P in feces. Decomposing litter represents the main source of nutrient return to the pasture, especially calcium, phosphorus, and nitrogen. tropics 2009 paddocks. paddocks . (paddocks) 40 80 kg ha1.year1, ha1year1 hayear ha 1.year 1, 1 year ha-1.year-1 L day1. day1 day 1. day-1 feces material Mg calcium phosphorus 200 (paddocks 4 8 ha1 year1 ha1.year1 ha1year 1year ha-1.year- day- 20 ha1.year ha-1.year

This study determined the effects of rumen-protected methionine (RPMet) supplementation on milk yield and milk composition in early lactation dairy buffalo fed a forage-based diet. A total of 20 lactating, multiparous Anatolia water buffalo were used, with a mean initial milk yield of 4.63 ± 0.52 kg/d, 42.75 ± 6.21 days in milk, and a body weight of 452.8 ± 28.92 kg. The buffalo were separated into two groups, each containing 10 animals of similar body weight, parity, days in milk, and milk yield. The first group (CON) received a ration without feed additives as a control, whereas the second group (RPMet) was fed the control diet supplemented with 10g/head/day of RPMet. The buffalo were housed in two separate free-stall barns. The experiment lasted for nine weeks, including one week for adaptation and eight weeks for the trial period. Experimental animals were fed a total mixed ration with a forage to concentrate ratio (R:C ratio) of 70:30 containing 15% crude protein and 1.72 Mcal/kg NEL. Daily milk yield was recorded for individual animals and milk samples were collected at 2-w intervals. The supplementation with 10 g/d of RPMet considerably increased milk yield (+ 0.16 kg/d), FCM (+ 0.66 kg/d), energy-corrected milk (+ 0.74 kg/d), milk protein yield (+ 0.02 kg/d), and milk fat yield (+ 0.05 kg/d), but did not affect milk lactose and SNF yield. A higher milk protein percentage was obtained with RPMet compared to the CON (0.23% vs.0.21); fat, lactose, and solid non-fat were similar. Early lactation RPMet supplementation beneficially affects milk yield, milk protein content and yield, and milk fat yield. Further studies are needed to assess the efficiency of RPMet under different dietary conditions in lactating buffalo.

The objective of the study was to determine, through deep learning, the predictability of milk yield from a cow's side-view, rear-view image, or a combination of the two. The data size of 1 238 image pairs (the side-view and rear-view images) from 743 Holstein cows in their first or second parity, and their corresponding first-lactation, 305-day milk yield values were used to train and test Deep Learning models. The data were first split into the training and testing data at a ratio of 80:20, respectively. The training data were augmented four times, then again divided into training and validation data at the ratio of 4:1, respectively. Three principal analyses were done, the prediction of milk yield using rear-view images, using side-view images, and using a merge of the side-view and rear-view images. In all three analyses, poor predictions were observed, i.e., R² values ranging from 0.30 to 0.38, the mean absolute error ranging from 1112.9 kgs to 1148.3 kgs, the root mean square error values ranging from 1401.2 kg to 1480.5 kg, and the mean absolute error percentages ranging from 17.0 to 17.6%. Hypothesis tests were done to check whether there was any difference between these three prediction models. There was no significant difference in performance between the prediction models. It was concluded that predicting the 305-day milk yield of Holstein cows using either view had the same level of accuracy, and no additional benefits were derived from using both the rear and side views.

ABSTRACT The objective of this study was to examine the physicochemical composition and sensory properties of Boursin cheese made from the milk of goats fed diets with increasing levels of cassava chips replacing corn. Eight lactating Alpine goats were distributed into two 4 × 4 Latin squares, where they were subjected to diets in which 0, 33, 66, and 100% of corn was replaced with cassava chips. The cheeses were prepared with individual milk of each goat for physicochemical, yield, and texture analyses. Sensory analysis consisted of flavor and texture appraisal by 50 untrained tasters, using the difference-from-control test and the acceptance test. The cheeses from the four treatments did not differ in their fat, protein, and total solid contents; acidity; moisture; ash; pH; yield; or the texture parameters of gumminess, cohesiveness, hardness, and chewiness. They also showed no difference in the sensory acceptance of flavor and texture, indicating that the panelists did not perceive the replacement of corn with cassava chips. squares 0 33 66 100 yield analyses 5 tasters differencefromcontrol control fat protein contents acidity moisture ash pH gumminess cohesiveness hardness chewiness 3 6 10 1

The objective of the current study was to establish the possible impact of several non-genetic factors on milk yield. Data from 1120 lactations were collected between 2019 and 2022 regarding cows' milk yield (MY) and 305-d MY, under the influence of year, calving season, lactation order, type of calving, and calving ease. MY proved to be influenced by the season of calving, being higher in summer (5745.5 ± 156.24 kg) compared to spring (5448.9 ± 108.1 kg) or winter (5327.35±200.6 kg). A marked influence of the rank of lactation and type of calving were found. The maximum MY was found in the 4th lactation (6211.8 ± 210.18 kg), whereas the lowest MY was recorded in the 6th lactation (5535.8 ± 116.6 kg). No substantial effects for year and calving ease were recorded (6003.71 ± 174.23 vs. 5712.14 ± 163.9 for eutocic vs. dystocic births). Season, lactation order, and twinning substantially influenced 305-d MY. In conclusion, MY and 305-d MY proved to be highly dependent on environmental and management factors. By ensuring good management practices pre- and post-partum, the farmers can maintain the milk production at a high level.

RESUMO O objetivo do presente ensaio clínico foi avaliar o consumo de matéria seca (CMS) e o comportamento de vacas diagnosticadas com mastite clínica (MC) leve ou moderada, provocada por patógenos Gram negativos ou com cultura negativa. Os casos foram designados para o grupo controle negativo ou grupo tratamento, o qual recebeu uma infusão intramamária de ciprofloxacino por três dias consecutivos. O comportamento foi avaliado por meio de coleiras que monitoram os tempos de ruminação, de atividade e de ócio. Cochos eletrônicos foram utilizados para registrar o comportamento alimentar e o CMS. Além disso, a produção média diária de leite, a composição do leite, a contagem de células somáticas e a contagem de leucócitos também foram avaliadas. A partir de 67 casos de MC, 23 atenderam aos critérios de inclusão e foram designados para o grupo controle negativo (n=13) e para o grupo tratamento (n=10). Não foram encontradas diferenças no comportamento entre os grupos, durante o período experimental. Ademais, não houve diferença para o CMS, o comportamento alimentar e os demais parâmetros, entre o controle negativo e os casos tratados. Assim, o tratamento seletivo não trouxe impactos negativos sobre os parâmetros estudados. Essa estratégia terapêutica pode ser benéfica por reduzir custos e o uso de antimicrobianos, nas propriedades leiteiras. CMS (CMS MC (MC moderada negativa consecutivos ruminação ócio disso leite avaliadas 6 2 n=13 n13 n 13 (n=13 n=10. n10 n=10 . 10 (n=10) grupos experimental Ademais tratados Assim estudados antimicrobianos leiteiras n=1 n1 1 (n=1 (n=10 n= (n= (n

ABSTRACT The aim of the present negatively controlled, randomized clinical trial was to assess dry matter intake (DMI) and behavior in cows with mild and moderate naturally occurring CM caused by gram-negative or culture-negative pathogens. Enrolled cases were assigned to either the negative control or to the treatment group, which received one infusion of intramammary ciprofloxacin for three consecutive days. Behavior was assessed through neck collars which monitors rumination, activity, and rest times. Electronic feeders were used to record feeding behavior and DMI. Also, average daily milk yield, milk composition, somatic cells count (SCC), and white blood cells count (WBC) were evaluated. Of a total of 67 cases of CM, 23 met the criteria to enter the experiment and were enrolled to the negative control (n=13) and to the treated group (n=10). There was no difference in behavior between groups throughout the studied period. Also, no difference was found in DMI, feeding behavior and in the other parameters between negative control and treated cases. Therefore, the selective treatment did not have negative impacts on behavior and DMI, as well as in the other parameters. This therapeutic strategy can be beneficial since reduces costs and the use of antimicrobials in dairy farms. controlled DMI (DMI gramnegative gram culturenegative culture pathogens days rumination activity times Also yield composition SCC, SCC , (SCC) WBC (WBC evaluated 6 2 n=13 n13 n 13 (n=13 n=10. n10 n=10 . 10 (n=10) period Therefore farms (SCC n=1 n1 1 (n=1 (n=10 n= (n= (n

Abstract Species of the genus Cynodon are among the most cultivated forage crops in the world due to their high yield and nutritional quality, and its use in cattle feeding has been associated with gains in animal weight and increased milk production. The objective of this study was to model covariance structures in Cynodon spp. clones and study the changes in ranking of the selected genotypes, since it is believed that affects the ranking of genotypes. A total of 202 genotypes were evaluated in an experiment conducted in an augmented block design with four replications and four harvests. The genotypes were assessed for plant height, green weight, percentage of dry matter, and plant vigor. Nineteen repeated measures models with different covariance structures were tested. The best-fitted model adopts the CORH covariance structure for the genetic effects. Correct modeling of the covariance structure affected the ranking of genotypes in all variables evaluated. quality production spp 20 harvests height matter vigor tested bestfitted best fitted effects 2

ABSTRACT High-production cows require facilities providing comfortable environments to enhance production efficiency and sustain milk quality. This study evaluated the impact of climatizing the feeding area post-morning and afternoon milking on environmental variables, thermal comfort indices, and the yield and quality of milk in lactating Girolando cows. The experiment followed a 4 × 4 Latin square design with four treatments across four experimental periods, using four cows per treatment. The post-milking climate control treatments included: shading; shading + ventilation; shading + ventilation + shower; and an evaporative adiabatic cooling system. The evaporative adiabatic cooling system proved most effective in maintaining thermal conditions near the comfort level for dairy cows, as indicated by lower thermal comfort indices. This system also enhanced morning and overall milk production. However, the climate control systems did not significantly affect the contents of protein, fat, or lactose in the milk. Highproduction High postmorning post variables indices periods treatment postmilking included shower However protein fat

RESUMO As vacas de alta produção necessitam de instalações que ofereçam ambientes amenos, para que ocorra aumento da sua eficiência produtiva e manutenção da qualidade do leite. Dessa forma, esse trabalho objetivou avaliar a influência da climatização da área de alimentação após o período das ordenhas matutina e vespertina sobre as variáveis ambientais, índices de conforto térmico, produtividade e qualidade do leite de vacas girolando em lactação. Foi utilizado o delineamento em quadrado latino 4 × 4, com quatro tratamentos e quatro períodos experimentais, com quatro animais por tratamento, totalizando 16 repetições. Os tratamentos foram os sistemas de climatização na pós-ordenha: sombreamento; sombreamento + ventilação; sombreamento+ ventilação+ ducha e sistema de resfriamento adiabático evaporativo. O sistema de resfriamento adiabático evaporativo aumenta a produção leiteira na ordenha da manhã e na produção total. Os teores de proteína, gordura e lactose não foram influenciados pelos sistemas de climatização estudados. amenos forma ambientais térmico lactação experimentais tratamento 1 repetições pósordenha pós pós-ordenha ventilação total proteína estudados

Abstract This study examined the relationship between age at first calving and milk production in Holstein heifers within an intensive system in the dairy basin of Córdoba, Argentina. Retrospective data from 452 cows calving between 2016 and 2017, aged between 23 and 32 months, were collected. The results revealed a significant decrease in adjusted 305-day milk yield as age at first calving increased. Cows calving at 24 months yielded higher total milk production by the end of lactation compared to those calving at 31 and 32 months. A significant difference in daily milk yield during lactation was observed based on age at first calving, while no significant effect of calving year was found. Total daily milk yield was also influenced by age at first calving, with cows calving at 24 months exhibiting higher production compared to those calving at 32 months. The dry period, representing the days from drying off to the start of the subsequent lactation, was also influenced by age at first calving, with significant differences observed between cows calving at 23 and 31 months, as well as at 24 and 31 months. In terms of reproductive variables, a significant difference in the calving interval was found based on age at first calving. No significant interaction between age at first calving and calving year was identified for any of the analyzed variables. In conclusion, this study demonstrated that age at first calving has a significant impact on milk production in Holstein cows within an intensive system. The findings suggest that placing greater emphasis on achieving first calving between 23 and 25 months of age may enhance productive and reproductive efficiency in dairy farms.

Resumen Este estudio analizó la relación entre la edad al primer parto y la producción de leche en vacas Holstein en un sistema intensivo en la cuenca lechera de Córdoba, Argentina. Se recopilaron datos retrospectivos de 452 vacas que parieron entre 2016 y 2017, con edades comprendidas entre 23 y 32 meses. Los resultados mostraron que a medida que la edad al primer parto aumenta, la producción de leche ajustada a los 305 días disminuye significativamente. Las vacas que parieron a los 24 meses produjeron más leche total al final de la lactancia en comparación con aquellas que parieron a los 31 y 32 meses. Se observó una diferencia significativa en la producción diaria de leche en lactancia según la edad al primer parto, pero no se encontró un efecto significativo del año de parto. La producción diaria total de leche también fue afectada por la edad al primer parto, con las vacas que parieron a los 24 meses mostrando una mayor producción en comparación con las que parieron a los 32 meses. El período seco, que representa los días desde el secado hasta el inicio de la próxima lactancia, también fue influenciado por la edad al primer parto, con diferencias significativas entre las vacas que parieron a los 23 y 31 meses, y a los 24 y 31 meses. En cuanto a las variables reproductivas, se encontró una diferencia significativa en el intervalo entre partos según la edad al primer parto. No se encontró una interacción significativa entre la edad al primer parto y el año de parto para ninguna de las variables analizadas. En conclusión, este estudio demostró que la edad al primer parto tiene un impacto significativo en la producción de leche de vacas Holstein en un sistema intensivo. Los resultados sugieren que un mayor énfasis en alcanzar un primer parto a una edad entre los 23 y 25 meses podría mejorar la eficiencia productiva y reproductiva en las explotaciones lecheras.