Comparative efficacy of intrauterine oxytetracycline-metronidazole combination versus cephalexin in the treatment of repeat breeder cows

Introduction

Infertility and subfertility in dairy cattle represent significant constraints to herd productivity, extending calving intervals, increasing insemination costs, and heightening culling rates. Among these, the repeat breeding syndrome characterized by failure to conceive after three or more inseminations despite regular estrous cycles and apparently normal genital tracts is of particular economic and clinical concern [1] . One of the frequently implicated etiologies of repeat breeding is subclinical endometritis or uterine infection, which may not present overt clinical signs but can disrupt early embryonic survival or uterine receptivity [2,3] . To address this, intrauterine antibiotic therapy has long been employed under field conditions, often in conjunction with hormonal synchronization protocols. However, the choice of antibiotic whether to use a broad-spectrum agent, a therapy targeting anaerobes, or a combination remains debated, especially under diverse field settings. Previous studies have evaluated intrauterine use of oxytetracycline, gentamicin, cephalexin, and combination formulations, though results have been inconsistent. For instance, Parikh et al. [4] compared multiple intrauterine drugs in repeat breeder cows (including oxytetracyclinebased remedies). Kutty [5] reported favourable conception outcomes following intrauterine gentamicin infusion in repeat breeder cross-bred cows. In a comparative trial of intrauterine infusions, Mastalone-U (a multiantibiotic combination) at higher doses resulted in poorer conception rates than lower-dose controls or other agents, cautioning against indiscriminate use [6] . The incidence of subclinical endometritis among repeat breeders has also been documented: Kumar and colleagues [7] reported that cows with ≥ 4 % polymorphonuclear cells on cytology benefited variably from intrauterine antibiotic or herbal therapies. Despite these efforts, there is still a scarcity of direct comparisons between combinations targeting both aerobic and anaerobic flora (e.g. oxytetracycline + metronidazole) versus conventional singlespectrum agents like cephalexin, especially under real-world field conditions. Moreover, the rising issue of antimicrobial resistance underscores the need for evidence-backed antibiotic choices rather than empirical therapy [8,9] . In Kerala and much of India, where dairy farms operate under varied management conditions, there is a need for pragmatic, field-validated protocols for treating repeat breeders effectively. The present investigation was thus undertaken with the objective to compare the efficacy of intrauterine oxytetracycline-metronidazole combination versus intrauterine cephalexin (each combined with a standard synchronization + timed AI protocol) in repeat breeder cows under field conditions in Kozhikode district, Kerala. Through this comparative approach, the study seeks to address whether broad-spectrum + anaerobe coverage provides a meaningful advantage over a conventional cephalosporin in improving pregnancy outcomes in repeat breeding cattle.

Materials and Methods

The study was conducted on 12 crossbred cows with a history of repeat breeding presented at the Veterinary Dispensary, Thiruvambadi, Kozhikode district, Kerala. Animals had body score range from 2-3. Per-rectal examination revealed no palpable ovario-uterine abnormalities. Animals were randomly divided into two groups:  Group I (N=6): Treated with intrauterine cephalexin (4 g; Lixen).  Group II (N=6): Treated with a combination of oxytetracycline (30 ml; 50 mg/ml Zydus) and metronidazole (30 ml; 5 mg/ml, Metrogyl).

Antibiotics were administered during estrus, and the subsequent estrus cycle was discarded to allow for natural uterine cleansing. Ten days later, per-rectal examination was performed to identify a functional corpus luteum, following which prostaglandin analogue (500 µg) was administered intramuscularly. A second prostaglandin dose was given 11 days later. Artificial insemination was carried out on the 3rd and 4th days after the final prostaglandin injection. Pregnancy diagnosis was performed by rectal palpation 90 days after AI. Two groups were compared using independent two sampled ttest and graph was plotted (Graph Pad Prism 10.5).

Results

In the present study, none of the six cows treated with intrauterine cephalexin conceived, whereas 4 out of 6 animals (66.7%) treated with the oxytetracycline-metronidazole combination became pregnant and statistically significant (P=0.025; Figure 1). This outcome highlights the markedly superior efficacy of the oxytetracycline-metronidazole regimen in managing repeat breeding under field conditions.

Discussion

Infertility, particularly due to subclinical endometritis, is a leading contributor to reproductive inefficiency and economic losses in high-yielding dairy herds [3] . The subclinical nature of many uterine infections makes diagnosis challenging, prompting reliance on empirical intrauterine therapies aimed at improving uterine health and subsequent conception rates.

Oxytetracycline is widely recognized for its broad-spectrum antibacterial activity, particularly effective under the anaerobic conditions present within the postpartum bovine uterus [10,11] . In field studies, its combined use with prostaglandins has yielded positive outcomes in cows diagnosed with endometritis [12] . The addition of metronidazole, which is particularly effective against obligate anaerobes and protozoa, further broadens the antimicrobial coverage and enhances therapeutic efficacy. This synergistic approach may account for the higher conception rate observed in the present study. The use of prostaglandin analogues in both groups likely aided uterine involution and estrous synchronization, facilitating timed artificial insemination. Prostaglandins have previously been shown to improve fertility in cows with endometritis or a persistent corpus luteum [12,13] , aligning with the present protocol. In contrast, cephalexin, a first-generation cephalosporin primarily effective against gram-positive organisms, failed to improve conception in this cohort. Similar results have been reported by Parikh et al. [4] , where cephalexin showed limited efficacy in repeat breeder cows compared to other intrauterine agents such as gentamicin and oxytetracycline. The ineffectiveness of cephalexin in this study could be due to the presence of mixed or anaerobic bacterial populations in the uterine environment, against which cephalexin has limited action. Furthermore, the indiscriminate or prolonged use of antibiotics like cephalexin may contribute to emerging antimicrobial resistance, as reported in cephalexin-resistant Campylobacter strains isolated from livestock [9] . This underlines the importance of judicious antibiotic selection based on field efficacy and potential resistance profiles. Taken together, these findings underscore that a combination therapy targeting both aerobic and anaerobic pathogens such as oxytetracycline with metronidazole offers superior outcomes in treating repeat breeder cows. This approach, when integrated with appropriate hormonal protocols, may substantially improve fertility in field conditions. However, larger-scale studies are warranted to validate these findings and assess potential regional variations in antimicrobial resistance and bacterial flora.

Conclusion

The combination of oxytetracycline and metronidazole, when used along with sexual rest, timed artificial insemination, and double administration of prostaglandin, improved the pregnancy rate in repeat-breeding cattle. In contrast, cephalexin failed to produce positive results, suggesting that it is not a suitable intrauterine antibiotic choice under the field conditions of Thiruvambadi. The findings also raise the possibility of emerging cephalexin resistance in reproductive tract infections. Further field-based studies with larger sample sizes are required to confirm this resistance pattern and to establish effective therapeutic strategies for managing infertility in dairy cattle.

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