Mbwa is a 9/10 (N/N) animate noun. It is the same in both singular and plural. Because it is animate it follows 1/2 (M/Wa) agreements. Given we have mbwa wa Rashidi wanene, we can see mbwa is plural in this sentence.
Just a note that 9/10 animates are a bit funny in that the possessive tends to follow 9/10 rules (mbwa yangu = my dog, mbwa zangu = my dogs, rather than 1/2. This is because 1/2 nouns use the same agreement for singular and plural, and 9/10 nouns are themselves the same in singular and plural. This would lead to mbwa wangu being both "my dog" and "my dogs", so to avoid confusion they break the animate rule a little.
The English Wiktionary -nene entry states that it should be only used for people; and that for animals -nono is used instead. Can someone shed some light on the matter? Asante!