Srimad Bhagavatam Canto 05, Chapter 07, Text 05

SB 5.7.5

ije ca bhagavantam yajña-kratu-rupam kratubhir uccavacaih sraddhayahrtagnihotra-darsa-purnamasa-caturmasya-pasu-somanam prakrti-vikrtibhir anusavanam caturhotra-vidhina.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
With great faith King Bharata performed various kinds of sacrifice. He performed the sacrifices known as agni-hotra, darsa, purnamasa, caturmasya, pasu-yajña [wherein a horse is sacrificed] and soma-yajña [wherein a kind of beverage is offered]. Sometimes these sacrifices were performed completely and sometimes partially. In any case, in all the sacrifices the regulations of caturhotra were strictly followed. In this way Bharata Maharaja worshiped the Supreme Personality of Godhead.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Animals like horses and cows were offered in sacrifice to test the proper execution of the sacrifice. Otherwise, there was no purpose in killing the animal. Actually the animal was offered in the sacrificial fire to get a rejuvenated life. Generally an old animal was sacrificed in the fire, and it would come out again in a youthful body. Some of the rituals however, did not require animal sacrifice. In the present age, animal sacrifices are forbidden. As stated by Sri Caitanya Mahaprabhu:
asvamedham gavalambham
 sannyasam pala-paitrkam
devarena sutotpattim
 kalau pañca vivarjayet
“In this Age of Kali, five acts are forbidden: the offering of a horse in sacrifice, the offering of a cow in sacrifice, the acceptance of the order of sannyasa, the offering of oblations of flesh to the forefathers, and a man’s begetting children in his brother’s wife.” (Cc. Adi 17.164) Such sacrifices are impossible in this age due to the scarcity of expert brahmanas or rtvijah who are able to take the responsibility. In the absence of these, the sankirtana-yajña is recommended. Yajñaih sankirtana-prayair yajanti hi sumedhasah (Bhag. 11.5.32). After all, sacrifices are executed to please the Supreme Personality of Godhead. Yajñartha-karma: such activities should be carried out for the Supreme Lord’s pleasure. In this Age of Kali, the Supreme Lord in His incarnation of Sri Caitanya Mahaprabhu should be worshiped with His associates by performance of sankirtana-yajña, the congregational chanting of the Hare Krsna mantra. This process is accepted by intelligent men. Yajñaih sankirtana-prayair yajanti hi sumedhasah. The word sumedhasah refers to intelligent men who possess very good brain substance.
Srimad Bhagavatam Canto 05, Chapter 07, Text 04
Srimad Bhagavatam Canto 05, Chapter 07, Text 06