The A1/A2 ß-casein genotype of cows, but not their horn status, influences peptide generation during simulated digestion of milk.

The effect of the horn status of cows on their milk composition and quality is a controversial research topic. In this study, 128 milk samples from 64 horned and 64 disbudded Brown Swiss and Original Braunvieh cows were collected from alpine farms where both horned and disbudded cows were grazing on mountain pastures. The samples were analyzed for their detailed composition and protein digestion in a simulated in vitro digestion (INFOGEST). To exclude probable influences on digestion, the ß-casein genotype with its variants A1 and A2 was also included in the study. The effects of horn status and ß-casein genotype were investigated in linear mixed models, which included additional influencing random factors such as Original Braunvieh blood proportion, stage of lactation, and farm. Horn status did not have any effect on milk composition or digestion. In contrast, milk from A1A1 cows showed a different protein digestion than milk of A1A2 and A2A2 cows in the gastric phase, including smaller amounts of ß-casomorphin(BCM)21-associated peptides and larger amounts of BCM11-associated peptides. Abundances of BCM7 did not differ between ß-casein genotypes. At the end of the intestinal phase, the digested milk of A1A1 and A2A2 b-casein genotypes did not differ.

Influence of dietary fiber content and horn status on thermoregulatory responses of Brown Swiss dairy cows under thermoneutral and short-term heat stress conditions.

In the present experiment, 10 horned and 10 disbudded mid-lactating Brown Swiss cows were included in a crossover feeding trial with a hay or hay and concentrate diet. The effects of dietary neutral detergent fiber (NDF) content and horn status on thermoregulatory responses under thermoneutral and short-term heat stress conditions were studied, as both are considered to ease the cow's thermoregulation under an environmental heat load. Cows received either ad libitum hay and alfalfa pellets (85:15, C-, NDF content: 41.0%) or restricted amounts of hay and concentrate (70:30, C+, NDF content: 34.5%). The level of restriction applied with the C+ diet was determined from pre-experimental ad libitum intakes, ensuring that both diets provided the same intake of net energy for lactation (NEL). For data collection, cows were housed in respiration chambers for 5 d. The climatic conditions were 10°C and 60% relative humidity (RH), considered thermoneutral (TN) conditions (temperature-humidity index (THI): 52) for d 1 and 2, and 25°C and 70% RH, considered heat stress (HS) conditions (THI: 74), for d 4 and 5. On d 3, the temperature and RH were increased gradually. Compared with TN, HS conditions increased the water intake, skin temperature, respiration and heart rates, and endogenous heat production. They did not affect body temperature, feed intake, or milk production. Lowering dietary fiber content via concentrate supplementation lowered methane and increased carbon dioxide production. It did not mitigate physiological responses to HS. Although the responses of horned and disbudded cows were generally similar, the slower respiration rates of horned cows under HS conditions indicate a possible, albeit minor, role of the horn in thermoregulation. In conclusion, future investigations on nutritional strategies must be conducted to mitigate mild heat stress.

The ACTH challenge and its repeatability in fattening bulls-influences of physiological state, challenge time standardization, and horn status.

Adrenocorticotropic hormone (ACTH) challenges are frequently performed in repetition when evaluating stress or welfare in animals. To our knowledge, the repeatability of ACTH challenges in cattle, although fundamental to further studies of this type, has not yet been the subject of research. Therefore, the objective of this study was to evaluate the repeatability of ACTH challenges in fattening bulls of different horn status. Eight-one bulls were subjected to 3 consecutive ACTH challenges. The first challenge (C1) was performed in calves aged 1.5 mo. Subsequently, animals were characterized as high or low cortisol responders and either disbudded or left with horns. They were then assigned to 1 of 3 rearing groups: a horned group (H+), a disbudded group (H-), and a mixed group (M; 50% horned and 50% disbudded), with each group containing an equal number of high and low responders. The second ACTH challenge (C2) was performed at the age of 11 mo. Time of day (TOD) of challenge was either fixed (ST = same TOD) or alternated (AT = alternate TOD) between C1 and C2. The third ACTH challenge (C3) was performed 7 d after and at the same TOD as C2. Saliva samples were taken 60 and 30 min before and 30, 60, 90, 120, and 150 min after each intravenous ACTH injection. The area under the curve (AUC) was calculated with respect to both ground (AUCG) and to increase (AUCI). The AUCI increased markedly between C1 and C2 (P < 0.05) in ST bulls, and no effects were observed for AUCG between C1 and C2 in ST or AT bulls, nor for any AUC between C2 and C3 (P > 0.1). The overall repeatability of AUCG and AUCI between C1 and C2, reflecting the repeatability between 2 different physiological states, was poor and moderate, respectively, for ST bulls (AUCG: r = 0.24, P > 0.1, intraclass correlation coefficient (ICC) = 0.21; AUCI: r = 0.48, P < 0.01, ICC = 0.41) and lacked in AT bulls (AUCG: r = 0.07, P > 0.1; ICC = 0.03; AUCI: r = 0.08, P > 0.1, ICC = 0.06). The repeatability of AUCG and AUCI between C2 and C3, reflecting the repeatability within the same physiological state, was moderate (AUCG: r = 0.59, P < 0.001; ICC = 0.53; AUCI: r = 0.58, P < 0.001, ICC = 0.52). Assignment to high and low responder groups based on peak cortisol concentration in C1 did not persist over time. H+ bulls showed higher AUCI in C2 and C3 (P < 0.1 and P < 0.05, respectively) than H- bulls. The M group differed from the H- group only in C3 (P < 0.05). Thus, the effect of horn status on ACTH challenges needs further investigation. In conclusion, our results report poor repeatability of the cortisol response to ACTH challenges for challenges performed in different physiological states and moderate repeatability for challenges performed within the same physiological state. Moreover, they point out the importance of standardization of TOD when performing repeated ACTH challenge.

Pre-slaughter stress and horn status influence physiology and meat quality of young bulls.

The study used 81 young bulls, half of which were disbudded at 7 weeks of age. The effects of horn status during rearing and of acute physical and emotional stress just before slaughter on the physiological status at slaughter and subsequent meat quality were investigated. Bulls were reared in groups containing i) only bulls with horns, ii) only bulls without horns, or iii) mixed (half with, and half without horns). Bulls of each rearing condition were assigned to one of two slaughter conditions: with limited (LS) or with supplementary stress (SS). LS resulted in lower heart rates, stress hormone concentrations and carcass temperature, whereas SS resulted in faster post mortem pH decline and lower juiciness. Horned bulls from unmixed rearing groups had lower early pm temperature, shorter sarcomeres, and lower tenderness compared to disbudded bulls. Correlations and regression analysis revealed relationships between physiological indicators, mainly heart rate before slaughter, and meat quality, including water-holding capacity and indicators of proteolysis.