Incidence du stress thermique sur la reproduction et les performances des élevages bovins laitiers algériens

Abstract

Climate variations are pronounced across the Mediterranean, particularly in Algeria, where this study evaluated the impact of environmental challenges on dairy cattle reproduction and production. In the first study, we investigated the relationship of Temperature-Humidity Index (THI) in the day of Artificial Insemination with fertility, evaluated by total pregnancy rate, (TPR), Conception Rate at 1st and 2nd Artificial Insemination (CR1stAI, CR2ndAI), repeat breeding (RBC), Conception Risk (CR), Services per Conception (SPC), and reproductive period (RP). The results show that severe THI (>80) reduced PR (-26%) in Brown Atlas cows and THI > 72 negatively affected CR1stAI and CR for imported breeds (Prim’Holstein: -49.7% and -17%, Montbéliarde: -20.7% and -15%, respectively), with hot season showed lower levels than colder season, and higher levels in areas with more comfortable THI. CR1stAI for Brown Atlas cows decreased by 43.9% and 46% for 68 <THI<71 and THI>80, respectively, with no significant effect on CR2ndAI and RBC. SPC rose significantly under heat stress (HS) (Prim’Holstein: 6.3%, Montbéliarde: 7.1% for THI>72), in harsher agroecological regions (Ar: Prim’Holstein: 30.9%, Montbéliarde: 26%). SPC increased in brown atlas breeds 0.073 for each incremental point in THI above 68. RP extended with higher THI (Prim’Holstein: +4.1%, Montbéliarde: +7.4%) and in warmer regions (Prim’Holstein: +122%, Montbéliarde: +73.4%) but shortened in autumn (Prim’Holstein: -15.3%, Montbéliarde: -8.4%). In the second study, we evaluated the impact of heat stress on animal’s behavior and physiological parameters (rectal temperature (RT), respiratory frequency (RF), cardiac frequency (CF), ruminating time, lying time, and shad-seeking behavior) with particular emphasis on milk quality, and udder health specifically subclinical mastitis (SCM). Results showed that high THI increased RT (0.016°C), CF (0.654 bpm), and RF (0.498 breaths/unit THI), while reducing ruminating (-0.144 min) and lying times (-0.119 min/unit THI) and increasing shade-seeking behavior (OR=3.35), the season effect interacted by high THI levels further compromised the results. Furthermore, milk quality deteriorated at high THI, particularly in protein (0.0073%), SNF (0.022%), lactose (0.012%), and salts content (0.0019%), with stability of other component including, fat and density, the season effect interacted by high THI levels further compromised the results, while subclinical mastitis (SCM) was more frequent at low THI (OR= 0.277 et 0.093 for quarters and individual cows, respectively). With no relationship between animal physiological parameters and behavior, except RT (P<0.05), and SCM. This research highlights the need for adaptive strategies to mitigate climate stress on cattle productivity across breeds and regions. These include genetic optimization for heat tolerance, environmental management protocols, advanced reproductive technologies, and targeted hormonal interventions to maintain productive and reproductive efficiency across diverse climatic conditions.